SB 945 
.G9 R3 
Copy 1 




THE 



WILT DISEASE, OR PLACHERIE, 



OF 



THE GYPSY MOTH 



^ 



How to aid the Spread of this Disease 



i» 



By WILLIAM SEIFF, Bussey Institution of Harvard University, 

under the direction of F. W. MNE, 

State Forester 



THE "WILT DISEASE," OR "FLACHERIE, 



n 



OF 



THE GYPSY MOTH. 



WILLIAM REIFF, 

BUSSEY INSTITUTION OF HARVARD UNIVERSITY. 



UNDER THE DIRECTION OF 



F. W. RANE, STATE FORESTER. 




BOSTON : 

WRIGHT & POTTER PRINTING COMPANY, STATE PRINTERS, 

18 POST OFFICE SQUARE. 

1911. 



<^ 






Approved by 
The State Board of Publication. 






CONTENTS 



Introductory, ............ 5 

I. Caterpillar Diseases in General, ...... 7 

Common Diarrhoea; Bead Disease; Muscardine ; Pcbrine; 
Flacherie. 

II. Resum6 of Some Experiments with Flacherie in 1909, ... 12 

III. Flacherie Experiments in 1910, . . . . . . 14 

A. General, ......... 14 

Acknowledgments; General Points of the Work; Con- 
trol Experiment. 

B. The Single Experiments, ...... 20 

Concord, North Carver, Boxford, West Bedford, Haver- 
hill, Marshfield, Kingston, Brockton, Beverly, Co- 
hasset, Hingham, Byfield. 

IV. Summary, .......... 53 

V. Final Conclusions, ......... 55 



INTRODUCTORY 



Anything that offers promise of being effective in our war- 
fare against the gypsy moth is hailed with delight by our 
Massachusetts people. 

It is with pleasure that the State Forester is able to offer 
this publication, setting forth the work with the " wilt disease," 
or " Flacherie," of the gypsy moth, which has been carried on 
during the past two years by Mr. William Reiff, under the 
supervision of Prof. W. M. Wheeler of the Bussey Institution 
of Harvard University. Professor Wheeler's co-operative in- 
terest in the moth-suppression work in the State is highly appre- 
ciated by the State Forester, and the results shovni in this 
bulletin will prove, we are sure, of great interest generally. 

This bulletin is a companion, in a way, to that issued on 
parasites, in that it is another method of attacking our foe. 
W^e desire to have as many strings as possible to our bow in 
fighting this pest. That this " wilt disease " is a most hopeful 
remedy there is little question. We anticipate carrying on 
even more extensive work with it the coming season. 

Upon reading this bulletin it will be readily apparent that 
any one can easily assist in furthering this work at little, if 
any, expense; and it is to be hoped that many will not only 
acquaint themselves with the methods employed, but experi- 
ment on their own initiative. If the State Forester can assist 
you in any way do not hesitate to call upon him. 

Acknowledgments. 

The experimental work and writing up of the data in this 
bulletin was done by Mr. William Reiff of the Entomological 
Laboratory of the Bussey Institution of Harvard University. 

The State Forester decided that the work undertaken by 
Mr. William Reiff durino; the season of 1909 was well worthy 



6 

of being continued uj)on a much larger scale, and co-operative 
jolans were happily agreed upon with Dr. Wheeler, with the 
results as outlined in this bulletin. 

Besides Professor Wheeler and Mr. Eeiff, there are the field 
agents and local superintendents of the regular moth staff, 
who made it possible to get results. To these we are also under 
obligations for their loyal support and co-operation. 

F. W. EANE, 

State Forester. 
Boston, Mass., March 21, 1911. 



THE "WILT DISEASE," OR "FLACHEEIE," OF 
THE GYPSY MOTH.' 



I. Caterpillar Diseases in General. 

The production of diseases is one of nature's methods of 
quickly checking the overproduction of living things. Animals, 
including man, and plants all have their own specific infec- 
tious diseases, which usually appear whenever a species be- 
comes so numerous that it menaces the prosperity of the 
coming generations. In the animal kingdom the possibility 
of overproduction is especially apt to occur in insects, since 
they form by far the largest portion of the world's fauna, 
and have a high rate of reproductivity. Insects, small though 
they are individually, form in their totality an immense mass 
of living matter. Of this mass we can get only a slight con- 
ception, even when we consider that insects are everywhere 
pj-esent, not only as a few scattered individuals, but in such 
enormous numbers that they constitute, as it were, a world in 
themselves. We may say without hesitation that among all the 
conditions which arise from and are caused by animals, there 
is none more widely distributed, more many-sided and which 
interferes more deej)ly with life on our planet than that which 
is brought about by insects. As Graber says : — 

Man may unwisely neglect these creatures — as he does many things; 
but their power for evil crushes him the more; indeed, it may destroy 
him if he persists in his neglect. 

Now, such a power may be checked by nature by one of the 
most efficient means which she possesses, — the infectious 
diseases. 

Owing to the profound influence which insects exert upon us 
and our culture, attention has been drawn to their diseases. 
A close study has been made of some of these; especially of 

1 Contributions of the Entomological Laboratory of the Bussey Institution, Harvard Uni- 
versity, No. 36. 



8 

those known to occur in the silkworm {Bombyx mori) and in 
the "nun" moth (Psilura monacha), which latter destroys the 
forests of Central Europe. 

The first scientific knowledge which we have of caterpillar 
diseases we owe to the valuable investigations of the French 
scientist Pasteur. Since his time many other investigators have 
been engaged in this study, among them the Germans Standfuss 
and Emil Fischer, the Italians Verson and Bolle, and the 
Americans Snow and Forbes. By their experiments and in- 
vestigations we are now able to recognize the character of the. 
more common caterpillar diseases. 

We may mention some of those diseases with which the 
lepidopterist will come in contact in the course of a few years. 

A very frequent disease of caterpillars is the common 
diarrhoea, which is produced in most cases by too juicy or too 
wet food. This is shown by the unusually wet excrement, the 
fluid part of which is green. If the disease is of longer stand- 
ing, the excrement does not cling together, but is voided as a 
pulpy mass, in which the single vegetable particles swim around 
undigested. This disease in itself is not dangerous, since it 
is not infectious, but it may prepare the way for the attack of 
other infectious diseases, which will be mentioned further on. 

In another disease, which has no popular name as yet, and 
which I shall call bead disease, the excrement masses hang 
from the body like a string of beads. This intestinal disease 
is probably due to unhealthy food, but the specific cause has 
not been determined. Apparently this disease, too, is not 
infectious. 

Of much greater importance is the disease known as muscar- 
dine. This is really a collective name for a series of fungous 
diseases, which convert the infected caterpillar in a short time 
into a stiff, swollen mass, with the skin invested with a grayish- 
white coating. Very hairy caterjjillars are especially suscep- 
tible to muscardine, but in extremely wet years even smooth 
caterpillars suffer from fungous diseases. It is easy to deter- 
mine whether muscardine is present in a given locality because 
the diseased caterpillars crawl toward the exposed tops of grass 
blades, poles or stems, and remain there after death, thus be- 



coming visible for a considerable distance. On a trip which I 
made in June, 1910, to Eaymond, N. H., I saw thousands of 
brown-tail moth caterpillars dead from muscardine, and com- 
monly hanging in this characteristic manner. Since these 
fungous diseases are extremely infectious, and propagate with 
incredible swiftness, and since healthy caterpillars are much 
inclined to gnaw at dead ones, the artificial production and 
propagation of muscardine has been hopefully considered dur- 
ing the last few years as a means of destroying the brown-tail 
moth. 

There are two fungi, especially, which are responsible for 
the death of most caterpillars ; these are Botrytis hassiana Bals 
and Entoniophthora aulicae Reichhardt. Experiments with 
fungous diseases of the brown-tail moth are being conducted by 
Mr. A. T. Speare, under the direction of Dr. E. Thaxter of 
Harvard University.^ 

The pehrine or pehrina, which has become so notorious 
through the great damage it has caused to the silk industry, 
is the caterpillar disease which has been studied so far most 
thoroughly. Caterpillars with this disease always have a 
wet anus, and if they are hairy, the hairs on this region of 
the body stick together. Smooth caterpillars also change their 
color considerably ; for instance, green caterpillars turn yellow- 
ish, and are often mottled with dark, irregular spots ; gayly 
colored caterpillars lose their brilliancy. This disease does 
not kill in a few hours or days, but the infected caterpillars 
languish slowly, lose their appetite, and become transparent 
and ill-nourished. They then shrink more and more, till 
finally at death only the fiabby dry skin remains. Pebrine 
appears preponderatingly in wet years, and its cause seems to 
be lack of nourishment. The specific cause, however, the dis- 
position, has not yet been absolutely determined. The carriers 
of the disease are known under the name Corpiiscoli di Cornalia, 
and have been described by Lebert ^ as the fungus Panhisto- 
phyton ovatiiin (Micrococcus ovatus). Here it might be of 
interest to cite from a review in " Deutsche Entomologische 

• "Seventh Annual Report of the State Forester of Massachusetts, " 1910, pp. 98-101. 
2 "Berliner Entomologische Zeitschrift," 1858, p. 170. 



10 

I^atioiial Bibliotbek," Iso. 3, Jalirg. II., 1911, where it is 
stated that the botanist ISTaegeli described the carrier of the 
pebrine, as early as 1857, as Nosema hombycis. This review, 
moreover, mentions the fact that W. Stempell (38. Jahresber. 
Zool. Sekt. Westf., Prov. Yer. f. Wiss. u. Kunst, 1909-10, p. 37) 
has made artificial infection experiments with this parasite, 
and found that it develops with extreme rapidity and great 
virulence, not only in caterpillars of the silkworm, but also 
in caterpillars of several local species of the same family. Thus 
Stempell reached the conclusion that this susceptibility of the 
individuals towards the pebrine parasite might be used prac- 
tically in combating injurious caterpillars. He further men- 
tions that his researches on this and other Microsporidia are of 
biological interest, since it would seem that there must be 
organisms so minute that they cannot be seen, even Avitli our 
most modern optical instruments. In several infectious diseases 
the carriers of the disease have not yet been optically demon- 
strated, and it may be that these carriers are such small 
organisms. These little oval shining bodies are now no longer 
regarded as plant organisms, but as belonging to the Psoro- 
sjjermii, a group of Protozoa. Pebrine is extremely in- 
fectious, and is carried over, as Pasteur has proved, from gen- 
eration to generation in the eggs, with increasing destructive- 
ness. 

We come now to the last and jDrobably most important of 
all the common caterpillar diseases, the disease called FlacJierie, 
Flaccidenza or caterpillar cholera, and in America known also 
under the name " wilt disease." This disease is characterized 
as follows : a caterpillar suffering from it soon stops eating, 
becomes weak and lazy, and usually crawls up on some object, 
as the trunk of a tree, a fence, a wall, or other vertical surface, 
where it remains without motion. In a few hours there drops 
from its mouth and anus a dirty, blackish, foul-smelling liquid ; 
the caterpillar becomes more and more flaccid, one leg after the 
other looses its support, and finally the creature, reduced to a 
black skin, hangs dead, still holding on with one or two of its 
false feet or with the anal claspers. The slightest touch now 
suffices to break the skin, and a thin, dark, offensive-smelling 



n 

liquid flows out. Flacherie kills the older more q^^icklv than 
the younger caterpillars. Young caterpillars, indeed, often 
live several days before they are killed by the disease. It is 
not positively known what organisms produce Flacherie. The 
bodies of caterjDillars which have died of this disease show ex- 
tremely small bacilli, innumerable schizomycetes, and, more 
particularly, many small strings of micrococci ; but which of 
these micro-organisms, if any, is the real carrier of the disease 
is still unknown to specialists.^ To the investigations of Dr. 
E. Fischer, in Zurich, Switzerland, we owe considerable infor- 
mation regarding the primary causes leading to Flacherie, and 
the manner in which the disposition to this disease may be in- 
duced. He has pointed out that a decrease in the nutritive value 
of the food of the caterpillars, which induces a disturbance in 
their metabolism, is the first condition leading to the contraction 
of the disease. As a result of these disturbances the organisms 
responsible for the disease immediately find conditions suitable 
for their growth. One of the main causes of the disease is 
therefore to be sought in the predisposition of the caterpillars, 
while the specific infection of Flacherie is to be regarded as 
coming more or less secondarily; in other words, without this 
predisposition infection cannot take place, and the predisposi- 
tion can be brought about artificially by insufficient nourish- 
ment.^ Flacherie seems to be influenced by climate and weather 
conditions less than any other caterpillar disease. We meet 
with it both in the old and the new world, in wet, in dry and in 
normal weather. As a result of its comparatively great abund- 
ance and its extremely easy infection, Flacherie has become the 
" guardian angel " of the Central European forests. When the 
" nun " (Psilura monacha) makes its appearance in some places 
in Euroj)e in vast numbers, man with his wit and the powerful 
means at his command is quite unable to stop the destruction, 
but Flacherie always comes to his assistance. Although this 
disease has been much studied, it has not yet been positively 

' 1 Very recently C. Sasaki, in Tokyo, Japan, found that there were also polyhedral corpuscules 
present in caterpillars which were sick from Flacherie (" Deutsche Entomologische National- 
Bibliothek," Jahrgang II., 1911, No. 1, Referat). Since polyhedric corpuscules, however, are 
found chiefly in caterpillars which have been infected by the p^brine, a close relationship of these 
two diseases is highly probable. 

2 See Fischer's detailed accounts in the " Biologisches Centralblatt, " Band XXVI., No. 13-16. 
Leipzig, 1906. 



12 

established whether it is hereditary or not. There is at present 
no argument that can be brought against the heredity of the 
disease, while there are some important facts which indicate its 
heredity. These will be considered later. 

II. Resume of Some Experiments with Flacherie in 1909. 

Fischer called attention, in his excellent paper, already men- 
tioned, to the manner in which Flacherie can be artificially 
developed. He says that the disposition to the disease is 
secured by giving the caterpillars food which has been placed 
in water and renewed only every three or four days. This 
treatment apparently causes an injury to the leaf protoplasm, 
due to the presence of too much water, and there is a con- 
comitant increase in the acidity of the leaves.-^ If, now, a cater- 
pillar eats such leaves, the alkalinity of its digestive fluid, 
which is very strong in healthy individuals, decreases, and in 
this manner the first susceptibility to the disease is given. 
Before the visible outbreak of Flacherie, Fischer could recog- 
nize as an early symptom a characteristic sweet odor in the 
breeding cages, which could be compared best to that of some- 
what withered lilac blossoms. Whenever this odor was notice- 
able Flacherie soon made its appearance, and as it progressed 
the odor increased proportionately. Fischer recommends the 
artificial production of Flacherie among the caterpillars of the 
"nun" ("die ISTonne " of the Germans) by intentionally giv- 
ing the larvas this kind of food as soon as an abundance of the 
pest is noted in any particular locality. 

Bearing in mind the close relationship existing between the 
" nun " and the gypsy moth, I attempted during the summer 
of 1909 to put Fischer's conclusions regarding the artificial 
production of the wilt to a practical test. These experiments 
Avere published in detail in the entomological journal " Psyche," 
Vol. XVI., ISTo. 5, October, 1909. There appeared also a Ger- 
man translation of the paper in the " Societas Entomologica," 
Jahrgang XXIV., pp. 178—181, Zurich, Switzerland. The 
main facts in these experiments are here noted. Up to 70 
per cent, of the caterpillars were killed by artificially produced 

* 1 See the experiments which Sasaki performed on mulberry trees in Japan, "Zeitschrift fiir 
Pflanzenkrankheiten," XII. Band, Jahrgang 1902, 4. Heft, pp. 203-226; 5. Heft, pp. 258-278. 



13 

Flacherie, while all caterpillars which were kept apart for con- 
trol remained healthy. From these resnlts I was therefore 
led to believe that the artificially produced Flacherie might be 
utilized as a valuable aid in the destruction of gypsy moth 
caterpillars. If the disease appears in nature during normal 
weather conditions, the caterpillars are in most cases almost 
full grown when attacked; but the farther the weather condi- 
tions of the year differ from the normal, the earlier in their 
life will the disease affect them. The fact that I succeeded in 
rendering the caterpillars susceptible to the wilt before the 
third molt suggested that this may be of importance in the 
practical use of the disease, since by artificially inducing 
Flacherie, relief might be had weeks sooner than happens in 
nature. 

Better to understand the conclusions drawn from the last 
experiment, which was performed on trees on which a consid- 
erable number of gypsy moth caterpillars occurred naturally, 
the following account is given : A group of oak and another of 
willow trees were infested with about 5,000 caterpillars each. 
Shortly before their fourth molt, upon each of these two groups 
of trees 100 sick and 50 dead caterpillars were destributed. 
The disease spread with amazing rapidity, and even on the 
following day many freshly killed caterpillars could be counted. 
By the time of pupation about 4,000 caterpillars on each group 
of trees had succumbed to the disease. Two conditions which 
did not enter into my previous experiments united to cause this 
unusual result. In the first place, the two groups of trees had 
been badly infested and injured by gypsy moth caterpillars 
the previous season, as was evidenced by the unhealthiness of 
the leaves during the summer of 1909, and the caterpillars had 
probably become predisposed to the disease on account of the 
resulting decrease in the value of their food. As a second 
very important factor may be mentioned the dry weather, 
which by its desiccating effect upon the leaves served to render 
the food for the caterpillars still less nutritious. Hence, from 
the beginning there was a decreased vitality in the tissues, and 
digestion was early disturbed. In short, the caterpillars were 
already very susceptible to the disease at the time I introduced it 



14 

among- them, and conditions were therefore most suitable for the 
spread of the wilt. Always in the places that have been injured 
by gypsy moth caterpillars in previous years, there is a pre- 
disposition on the part of caterpillars of the following year 
toward Flacherie. The heavy defoliation checks the normal 
metabolism of the attacked vegetation, which causes a weak 
and sickly development of the shoots, and these therefore do 
not furnish the caterpillars sufficiently wholesome nourishment. 
It should be remembered that these facts, in the long run, 
mean a self-protection of the vegetation. If at this time dead 
and sick material is introduced among the caterpillars in such 
a locality, the organisms of the disease will act readily upon 
the individuals present. Infection will take place even in 
cases where a locality is badly infested by the caterpillars for 
the first time, because one can always find a large number of 
weak and therefore susceptible specimens. Then, as the disease 
progresses, it acquires such virulence that even the previously 
healthy specimens become infected. 

In the article mentioned I called attention to other ways in 
which the caterpillars advance the infection among themselves, 
that is, during the resting period, during the feeding time, 
etc., and how easily the disease may be carried over by the 
caterpillar to its pupal stage. The great probability of an 
economic value in Flacherie for destroying the gypsy moth was 
suggested, but it was thought that the experiments of only a 
single year had better not be taken as a comprehensive method 
for the practical use of the wilt, and that further experiments 
should be undertaken on a larger scale to substantiate the 
obtained results. 

III. Flacherie Experiments in 1910. 

A. General. 
In the spring of 1910 the author was requested, by the State 
Forester of IMassachusetts, to make similar experiments on a 
large scale in different parts of the State. ^ These experiments 
were undertaken with the help and kind encouragement of 
Prof. W. M. Wheeler. I would also express my indebtedness 

I Cf.: "Sixth Annual Report of the State Forester of Massachusetts," 1909, p. 86. 



15 

to all those from whom I have received advice and actual 
assistance. My thanks are also due to State Forester Frank 
W. Kane and Assistant Forester L. H. Worthlej for much 
help ; and to their division agents, l^orman Souther of Bridge- 
•v^ater, and Francis C. Worthen of Georgetown, and to Mr. 
H. P. Richardson, local moth superintendent of Concord, for 
their support in the field work. Last but not least, I owe, 
through correspondence, several valuable hints to Dr. E. Fischer, 
Ziirich, Switzerland, who, through his investigations on insect 
diseases, is to be regarded the proper instigator of these ex- 
periments. 

In the beginning of the work each of the division agents was 
asked by letter to suggest convenient localities in which to con- 
duct the experiments. Three of the division agents stated 
that they had no suitable places in their districts. In the 
remaining divisions 29 places were chosen, but at the end of 
my investigations unfortunately 13 of these could not be used, 
since some of the local moth superintendents had not followed 
instructions, and other places had been sprayed with arsenate 
of lead. Isolated forest districts, varying from small areas 
to several acres, were chosen for the experiments. The isola- 
tion was for the purpose of making easier a control of the 
place, since in such a locality an eventual increase or decrease 
of the caterpillar mass by migration was less probable. The 
local superintendents of the different places were instructed not 
to use any artificial means for destroying caterpillars in the 
selected woods. I was, however, obliged to use some localities 
in which, during the preceding winter, some of the egg clusters 
had been killed by creosote. According to the size of the 
various places, the local superintendents were requested to col- 
lect a corresponding mass of gypsy moth caterpillars shortly 
before their second molt. These amounted to from 50 to 100 
individuals per acre. Where many egg clusters were present 
but few caterpillars had to be collected, and vice versa. Hence, 
the number of caterpillars to be collected was decided in ad- 
vance for each locality. The reason for this is that an in- 
fection spreads more easily and rapidly in a heavily infested 
district than in places less damaged by caterpillars. In a 



16 

badly infested forest of 10 acres or more the average number 
of caterpillars to be collected was placed at less than 50 speci- 
mens per acre, since the disease spreads best in such localities. 
The local superintendents had been instructed to feed the 
collected caterpillars daily with oak leaves, or with ajDple leaves 
where oak leaves could not be secured. These leaves were 
not to be removed from the twigs, and were to be placed in 
water for at least four days before feeding. A special em- 
phasis was laid on not giving as food leaves of trees which had 
been sprayed with arsenate of lead. As breeding cages com- 
mon wooden boxes were used, to which the entry of air was 
provided for by means of gauze coverings. Further, the local 
superintendents, who were not familiar with the wilt, were 
taught the character of this disease and its manner of appear- 
ance, and were instructed to communicate with me at once on 
the first appearance of Flacherie in their breeding cages. The 
local superintendents were asked to attend to this part of the 
work, since at that time it was not convenient to rear several 
thousand gypsy moth caterpillars in one j)lace, and also in 
order that their interest might be awakened in the experiments. 
As soon as the wilt was determined to be present in a brood 
the whole material was transplanted upon the previously chosen 
places, with the help of the respective superintendents. This 
was done as follows : a piece of clean cloth, burlap, for instance, 
about 2 feet long by 1 foot wide, was hung in dense foliage 
between the limbs of a tree, or from one tree to another close 
by (Fig. 1). In this hammock-like bag were placed, besides 
the dead and still living caterpillars of the brood, also all food 
remaining in the breeding cage, since such remains might also 
be supposed to contain organisms of the disease. 'No means 
were used to prevent the escape of the sick but still crawling 
caterpillars, in order that they might disseminate the organ- 
isms.^ Where possible, the bag with the material was hung 
about 6 feet or still higher from the ground, in order that the 
wind might aid in the spread of the disease. In planting 
the diseased material the direction of the prevailing wind of the 

* That this is the case is proved by some experiments which I shall consider particularly later, 
where only sick caterpillars were transplanted, but no dead caterpillars. 



17 

season was taken into consideration. For instance, in locali- 
ties which had prevailing east winds the infected material 
was exposed near the eastern border of the forest, but still 
inside of it, so that the wind, before reaching the larger part 
of the wood, was forced to strike first the center of the diseased 
area. It may be mentioned that in some cases, where no con- 
venient cloth was at hand, the breeding cages themselves with 
the material, after the removal of the cover, were hung between 
limbs. No difference was observed in the results. The in- 
fected material was planted in most of the localities at a time 
when most of the caterpillars in the field were undergoing the 




Fig. 1. — Method of hanging hammook in tree. 

third molt. The respective ages of the caterpillars will be 
mentioned under each experiment.^ 

It was important to select places which gave the best guaran- 
tee for the health of the growing caterpillars ; hence, special 
attention is called to the fact that in the experimental localities 
no disease is known to have occurred among the caterpillars 
of previous years. 



' I had always planned to plant the disease as soon as it made its appearance in one or the other 
of the broods. This was, however, frustrated on several occasions by various circumstances. 
For instance, some local superintendents did not notice the Flacherie till after the disease had 
prevailed for several days. It was, further, not always possible for me to depart immediately 
upon receiving a communication concerning the outbreak of the disease. It was also almost 
impossible for one man to transplant the infected material to all the chosen places during the 
short time in which the gypsy moth caterpillars were in the third or beginning of the fourth stage. 
This is the reason why in some localities the disease was planted later, although the caterpillars 
were already beyond the third molt. 



18 

After the eggs were laid in the autumn of 1910 all localities 
were carefully inspected, and the number of the fresh clusters 
was determined as nearly as possible. For examination of the 
single eggs, five clusters, when possible, were collected from each 
locality. Five clusters from a place in the western part of 
Concord, Mass., served for control. These eggs must be con- 
sidered as normal because they come from a place in which 
positively no disease whatever has occurred. In collecting 
clusters for examination the first five found were taken; and 
were not taken at random. 

Every single egg of all these clusters was examined micro- 
scopically. This, it is true, required very much time, but it 
was nevertheless indispensable. The eggs were separated into 
three kinds : first, those that showed no signs of development of 
the embryo (empty or unfertilized eggs) ; second, those in 
which the more or less developed embryo had been killed before 
its complete development ; and finally, those which showed a 
perfectly developed embryo (normal and supposedly living 
eggs). In every case in which the egg could not be absolutely 
assigned to the second series it was counted with the third 
series.^ 

In the details of all the work everything which seemed to 
suggest the economic value of the wilt has been purposely re- 
garded from the most unfavorable standpoint, for the purpose 
of meeting any objections. When estimating the egg clusters 
from the selected localities there was always present either the 
division agent or the local superintendent, and at that time 
■written notes were made of these estimates before the intro- 
duction of the disease. In the spring we made the lowest 
possible estimate on the number of clusters present, while 
with the second estimate in the autumn, after the disease had 
produced its effect, the fresh clusters were estimated as liberally 
as possible. 

The average which resulted from the examination of the 
single clusters must not be taken as absolutely fixed, since the 
small number of the clusters examined admits of a variation 

1 The eggs of the control clusters could all be distributed with exactitude into the respective 
series. 



19 



from the mean in both directions. The main purpose of the 
experiments, however, was not to make mathematically exact 
calculations, but to find out in what manner and to what degree 
the gypsy moth may be infected by the wilt. For these pur- 
poses the calculations made should be sufficient, and the figures 
given will not be far from the real average. 

As to the control experiment, the average of eggs in a normal 
cluster was found to be 437. I am not aware that the eggs of 
a large series of normal clusters have ever been counted in order 
to establish an accurate average. In published reports the aver- 
age of eggs in a normal cluster is stated as " 400 to 500." 

Control Experiment, Concord, Mass. 
Five clusters were taken in the western part of this locality, 
\\here there certainly did not occur any disease among the gypsy 
moth caterpillars. These clusters, therefore, must be regarded 
as normal. The microscopic examination of the eggs of these 
clusters gave the following results : — 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, . ... 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



Cluster 1. 

543 =99.27 per cent., or about 
547 eggs. 



per cent., or about 1 per cent. 
99 per cent. 



Cluster 2. 

2!= .47 



per cent., or about .5 per cent. 

per cent. 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



. 424 =99.53 per cent., or about 99.5 
. 426 eggs. 

Cluster 3. 

3 1 

A \ — 1-74 per cent., or about 2 per cent. 

. 395 =98.26 per cent., or about 98 per cent. 

. 402 eggs. 

Cluster 4- 

o f = -93 per cent., or about 1 per cent. 
. 424 =99.07 per cent., or about 99 per cen1 



per cent., or about 99 per cent. 



428 eggs. 



20 



Cluster 5. 

Unfertilized eggs, ... - 1 _. , i . i ^ 

T-i -.1 1 J i_ o ^ = -79 per cent., or about 1 per cent. 

Eggs with dead embryos, . d J 

Eggs apparently alive, . . 377 =99.21 per cent., or about 99 per cent. 
Total, .... 380 eggs. 

The average of these 5 clusters is as follows : — 

Dead eggs, .... 4 = .92 per cent., or about 1 per cent. 
Eggs apparently alive, . . 433 =99.08 per cent., or about 99 per cent. 

Total, . . . .437 eggs. 

The results of this control experiment are used in estimating 
the departure from the normal of the egg masses in all the 
other experiments. 

B. The Single Experiments. 

Concord, Mass. 

Division Agent, Chas. W. Minot; Local Superintendent^ Henry P. 
Richardson. 

As a suitable place for my experiments, I located, on May 20, 1910, 
an isolated forest of about 2^4 acres, belonging to the estate of Mr. 
William Brewster. This place is situated in the eastern part of Con- 
cord, about half a mile west of the West Bedford railroad station. 
The forest consists mainly of oaks about twenty years old and of a 
group of pines about fifty years old, all mixed with brush; and along 
the border, especially on the northern part, are birches about ten years 
old. 

According to the local superintendent and to the owner, Mr. Brewster, 
the gypsy moth caterpillars were quite numerous during the summer 
of 1909. Both are certain that there was no disease among the cater- 
pillars. We estimated this place to contain about 10,000 clusters of 
eggs in May, 1910. 

On June 6 I received notice from the local superintendent that the 
wilt had appeared among the caterpillars which he had collected and 
fed according to instructions. Two days later I went to Concord, and 
found that some 10 caterpillars were already dead and the others were 
apparently very sick, as they remained motionless even when irritated. 
The superintendent had begun to feed the caterpillars on May 26, and 
had noticed the first dead specimen on June 5. Accordingly, he had 
succeeded in developing the wilt artificially in the course of eleven days. 



21 



With the assistance of the local superintendent the whole breeding 
material was immediately exposed in the western part of the selected 
forest. The distance from the ground to the material, which was hung 
between the limbs of a tree, was about 15 feet. The largest number of 
gypsy moth c'aterpillars in this locality were at this time in the third 
molt, or about to pass into this molt. The wilt soon spread over 
the whole forest, as was seen during occasional visits to the place 
by Mr, Richardson, Mr. Brewster and myself. On Sept. 7, 1910, the 
fresh egg clusters were estimated by the local superintendent and 
myself to amount to about 5,000. Often 4 or 5 of these clusters to- 
gether would not make more than 1 normal cluster; the actual number 
of eggs was thus much less than would have been present in the same 
number of normal clusters. 

The examination of 5 clusters which had been collected Sept. 7, 
1910, on Brewster's estate showed the following counts : — 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 1. 
3 ] 
^ . > = 9.66 per cent., or about 9.5 per cent. 

131 =90.34 per cent., or about 90.5 per cent 
145 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Cluster S. 

2\ 

„ > =7.43 per cent., or about 7.5 per cent. 

137 =92.57 per cent., or about 92.5 per cent. 
148 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster S. 

13 1 

,Q > =48.06 per cent., or about 48 per cent. 

67 =51.94 per cent., or about 52 per cent. 
129 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Cluster 4- 

r. \ = 8.64 per cent., or about^8.5 per cent. 
74 =91.36 per cent., or about 91.5 per cent 



81 eggs. 



22 



Cluster 5. 

Unfertilized eggs, . . - \ g^g ^^ ^^ ^^^^^ g 5 p^^. ^^^^ 

Eggs with dead embryos, . 5 J 

Eggs apparently alive, . . 69 =93.24 per cent., or about 93.5 per cent. 

Total, .... 74 eggs. 

Averaging these 5 clusters we have : — 

Dead eggs, .... 20 =17.24 per cent., or about 17 per cent. 
Eggs apparently alive, . . 96 =82.76 per cent., or about 83 per cent. 

Total, . . . .116 eggs. 

A normal egg cluster contains on an average 433 eggs (p. 20) which 
are apparently alive. Since the infested locality averages only 96 eggs 
Avhich are apparently alive per clustei-, 41/2 clusters are necessary to 
equal the size of a normal cluster. The number of the fresh clusters, 
estimated at 5,000, thus has to be reduced to about 1,100 clusters to 
compare with the 10,000 clusters present in the spring of 1910. The 
number of apparently vital eggs, therefore, is decreased to about 11 
per cent, through the action of Flacherie. 

The local superintendent informed me that the disease had also spread 
into the neighboring forest districts. By an extended walk through 
about 5 acres of these woods I learned that the wilt had operated in 
the same manner as in the first locality. He is of the opinion that 
the number of clusters in this 5 acres has been decreased to about 
15 per cent. Adjoining these woods there are about 15 acres of forest, 
in which the local superintendent found that all egg clusters which 
had been laid in the summer of 1909, and which had been deposited 
1 foot or more above the ground, had failed to produce caterpillars, 
that is, the eggs had remained unhatched; but the caterpillars had all 
emerged from those eggs in clusters placed less than 1 foot above the 
ground. I found that these statements corresponded very closely with 
the facts. Here and there I noticed a slight exception by occasionally 
finding either a high-placed cluster from which a few caterpillars had 
emerged, or I detected close to the ground a cluster from which only 
a portion of the caterpillars had emerged. These exceptions, however, 
were insignificant, for they represented in each case hardly more than 
10 eggs. 1 am unable, so far, to find any explanation for this peculiar 
occurrence. At first I thought that an egg i^arasite might have exerted 
its helpful power, but the examination of eggs from several clusters 
which had remained unhatched showed that almost all eggs contained 
a fully developed dead embryo, and no signs of a parasite could be 
found. The moisture of the soil cannot be made responsible, for bor- 



23 

dering this forest there is another with exactly the same soil, the same 
kind of trees and of the same age as the other place, and although 
these forests are separated only by a very broad road, in the latter wood 
the caterpillars of almost all egg clusters of 1909 had emerged from 
clusters that had been placed at any height on the trunks of the trees. 
There were exceptional cases of clusters, sometimes on the upper, some- 
times on the lower part of the trees, from which all caterpillars had not 
emerged, but there was no evidence of the peculiar condition that 
characterized the clusters in the place first mentioned. Whether any 
cateriDillar disease has any effect in this occurrence, I cannot now say. 
The solution of this question may come in the future from careful ob- 
servations at this particular locality.^ 

An extensive forest in the southwestern part of Concord was visited, 
in which, according to the information of the local superintendent, the 
wilt had broken out naturally. The peculiar conditions which Ave found 
here require a detailed descrijition of the locality and of the manner 
in which the disease operated. The largest part of the forest, about 
20 acres, is situated upon the ridge of a hill. On the east and west 
the hill slopes to wet meadows. On the north and south the hill gently 
passes over into level country, and it is bordered here by broad roads. 
The principal trees on the ridge of the hill are high pines about sixty 
to eighty years of age; brush is almost absent. The slopes are covered 
in large part with young oaks, Avhicli are much mixed with brush of 
different kinds. Now, while the forest of the whole ridge, including 
the northern and soutliern slopes, suffered considerably from injuries 
by gypsy moth cateriDillars during the summer of 1910, the eastern and 
western slopes M^ere exempt from this damage. Soon after the cater- 
pillars had passed the third molt Flacherie made its appearance among 
those feeding on the pines upon the ridge of the hill. The disease 
developed here so rapidly that probably all cateriDillai'S were killed, for 
we were unable, even by careful search in these 20 acres, on Sept. 7, 
1910, to find a single fresh cluster. The statement, therefore, seems 
justified that all caterpillars, at least all the females (100 per cent.), 
were here killed by tlie wilt. This very high number, however, was 
restricted to the forest upon the ridge of the hill. On the first trees 
of the northern and southern slopes fresh egg clusters were found, and 
the number of these increased as we went toward the plain. But the 
inspection of such dead catei'pillars as were observed showed that the 
wilt had also operated in the woods of these sIojdcs. The local super- 
intendent looked here for Flacherie, but it did not appear till the cater- 
l^illars were in their last stage. The reason for this behavior of the 
wilt might be that the ridge of the hill, with its high trees, was much 
exposed to the effect of the wind, and after Flacherie had once devel- 
oped it could be spread very rapidly along the ridge. On the northern 

' Similar observations, where eggs have not hatched, were made elsewhere by different per- 
sons connected with the moth work, but no definite observations, as at Concord, were reported. 



24 



and southern slopes, however, the wind could not strike so hard, and 
the spreading of Flacherie toward the plain, therefore, took place com- 
paratively slowly. Upon the eastern and western slopes, on account 
of the lack of caterpillars, the conditions necessary for developing the 
wilt were not present. 

A map of the place, sketched by Mr. Richardson (Fig. 2), which may 
aid in understanding the description, is given herewith. 




Fig. 2. — Experiment, Concord, INIass. A. Summit of liill, now cleared. B. 
Northern slope, infested. C. Southern slope, infested. D. Eastern slope, 
not eaten. E. Western slope, not eaten. F. Meadows. 

Five clusters were examined for comparison from the localities in 
■which Flacherie developed naturally. These were collected on a walk 
through the forest district at the southern end of the hill, and from 
different trees taken at random. The result was : — 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



UnfertiUzed eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 



Total, 



Cluster 1. 

4l 
,^ } =12.59 per cent., or about 12.5 per cent. 

139 =87.41 per cent., or about 87.5 per cent. 
159 eggs. 

Cluster 2. 

21 

r, ) = 5.30 per cent., or about 5 per cent. 

143 =94.70 per cent., or about 95 per cent. 
151 eggs. 



25 



Cluster 3. 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



., or about 2 per cent. 
., or about 98 per cent. 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



= 2.14 per cent 
229 =97.86 per cent 

234 eggs. 

Cluster 4- 

= 3.17 per cent., or about 3 per cent. 
122 =96.83 per cent., or about 97 per cent. 

126 eggs. 



Cluster 5. 

oo f = 12.93 per cent. 
256 =87.07 per cent. 

294 eggs. 



or about 13 per cent, 
or about 87 per cent. 



Averaging these 5 clusters we get this result: 



Dead eggs, 

Eggs apparently alive, . 

Total, 



15 = 7.77 per cent 
178 =92.23 percent 

193 eggs. 



., or about 7.5 per cent. 
., or about 92.5 per cent. 



We notice also that the egg clusters from this place, where the wilt 
developed naturally, are considerably less than the normal size, about 
2V2 clusters being equal to 1 normal cluster. This, and the fact that 
only 7.5 per cent, of the eggs would fail to hatch, while in the experi- 
ment 17 per cent, were dead, is probably due to the fkct that upon 
this southern slope Flaeherie appeared late and spread but slowly. 



North Carver^ Mass. 

Division Agent, John A. Farley,- Local Superintendent, Herbert F. Atwood. 

This locality was visited on May 9, 1910, with the insjoeetor of the 
southern districts of the State of Massachusetts, Mr. Norman Souther 
of Bridgewater, to find suitable places for the intended experiments. 
The gypsy moth does not occur here in such enormous numbers as in 
the northern parts of the State, but I wished to have some experiments 
at places where the gypsy moth has but recently gained a foothold. 

An isolated wood of about 2 acres, situated somewhat southwest from 
Makepeace's cranberry bog, was found to be a suitable place. It con- 
sists of pines about forty years old and of oaks about twenty to twenty- 
five years of age, with considerable brush. 



26 

The gypsy moth was discovered here for the first time during the 
winter of 1909-10, by finding egg clusters. Several of these clusters, 
unfortunately, had been already killed with creosote before my first 
visit, but there were present, according to Mr. Souther's and my esti- 
mation, about 25 clusters. Whether there was any disease among the 
caterpillars of the previous year could not be ascertained, but it is 
highly improbable, considering the youth of the colony and the large 
size of the clusters. 

On June 14, 1910, the local superintendent sent me word that 
wilt had made its appearance among the caterpillars which he had 
collected and fed according to instructions. I therefore went to North 
Carver on June 16, and found that in Mr. Atwood's colony about 
3 per cent, of the cateri^illars had already died of Flacherie. Most 
of those still living were very sick. He therefore had developed the 
wilt artificially after a feeding of about fourteen days. 

This same day, with the assistance of the local superintendent, a 
part of the breeding material was exposed on the western side of the 
selected place. The bag containing the material was fastened about 
8 feet from the ground, between young oak trees. Most of the cater- 
pillars of this locality had just passed the third molt. 

On Oct. 7, 1910, an extended search was made by the local super- 
intendent and myself, but only 4 fresla clusters could be found. The 
raicroscoi^ic examination of these 4 clusters resulted as follows : — 



Cluster 1. 

Unfertilized eggs, ... 5 1 

TT' -t-u A \ \^ oi f = 6.03 per cent., or about 6 per cent. 

Ivggs with dead embryos, . 21 J ^ ' * 

Eggs apparently alive, . . 405 =93.97 per cent., or about 94 per cent. 
Total, . . . .431 eggs. 



Cluster 2. 
Unfertilized eggs, ... 3 1 _ „„ " 

Eggs with dead embryos, . 18 / = ^'^^ P^' '^^*-' ^' ^^^^^ ^'^ P^' ''^°*- 
Eggs apparently alive, . . 375 =94.62 per cent., or about 94.5 per cent. 



Total, . . . .396 eggs. 

Cluster 3. 



Unfertilized eggs, ... 2 \ ^ ^_ , 

Eggs with dead embryos, . 8 / = ^"^^ P^^" ''^''^■' «^ ^^«^* ^"^ P^^ ^^"*- 

Eggs apparently alive, . . 205 =95.35 per cent., or about 95.5 per cent. 



Total, .... 215 eggs. 



27- 



Cluster 4- 

Unfertilized eggs, . . . 3\ u ^ ^o k 

T-, -iu J J V 10 ^ =13.38 per cent., or about 13.5 per cent. 

Eggs with dead embryos, . 18 j ^ ' ^ 

Eggs apparently alive, . . 136 =86.62 per cent., or about 86.5 per cent 

Total, . . . .157 eggs. 

Averaging these 4 clusters we get : — 

Dead eggs, . . . . 20 = 6.67 per cent., or about 6.5 per cent. 
Eggs apparently alive, . . 280 =93.33 per cent., or about 93.5 per cent. 

Total, . . . .300 eggs. 

Since, as we have seen, a normal cluster contains on the average 
433 eggs with apparently living embryos, the living eggs of these 4 
clusters, after the wilt did its work, amount to about 64.5 per cent. 
The egg clusters which were present in the spring of 1910 were esti- 
mated at about 25, while only 4 fresh clusters were found in the 
autumn of IfllO. The total number of all apparently living eggs was 
decreased in this locality to about 13 per cent., as comjiared with the 
number present in the spring of 1910. 

Another place for experiments, very similar to the last one, was 
selected in North Carver. This is a forest district of 3 acres, and is 
situated east of the cemetery on Wenham Street. The timber and 
brush here are the same as in the other locality, and the egg clusters 
of the gypsy moth were also flrst discovered here during the winter' 
of 1909-10. Unfortunately, several clusters were killed with creosote 
before my first visit. The clusters still present were estimated by Mr. 
Souther and myself at about 600. On account of the young age of the 
colony and the considerable size of the clusters probably no disease 
had appeared among the caterpillars of the preceding year. 

The remaining part of the wilt material was planted among the cater- 
pillars of this locality on the same day and in the same manner as in 
the first colony. Here, also, most of the caterpillars at this time had 
just undergone the third molt. 

The estimate of the fresh clusters, which was made by the local super- 
intendent and myself Oct. 7, 1910. was about 400, from which the first 
5 found were used for microscopical examinations. The result is as 
follows : — 

Cluster 1. 
Unfertilized eggs, ...-].,, , 

Eggs with dead embryos, . 12 / = ^'^^ P^' "^^*-' °^ ^^out 4 per cent. 
Eggs apparently aUve, . . 280 =95.89 per cent., or about 96 per cent. 

Total, . . . .292 eggs. 



28 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 



Cluster 2. 
„„ > =17.17 per cent., or about 17 per cent. 
193 =82.83 per cent., or about 83 per cent. 

233 eggs. 

Cluster 3. 

= 7.38 per cent., or about 7 per cent. 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



113 =92.62 per cent., or about 93 per cent. 
122 eggs. 
Cluster 4- 



14 



= 4.89 per cent., or about 5 per cent. 
292 =95.11 per cent., or about 95 per cent. 

307 eggs. 
Cluster 5. 



9 



= 2.95 per cent., or about 3 per cent. 



362 =97.05 per cent., or about 97 per cent. 
373 eggs. 



Averaging' these 5 clusters we get : — 



Dead eggs. 

Eggs apparently alive, . 

Total, 



17 = 6.42 per cent., or about 6.5 per cent. 
248 =93.58 per cent., or about 93.5 per cent. 

265 eggs. 



Since this place, after infection with Flacherie, contains on the 
average only 248 eggs with apparently living embryos per cluster, 
almost 2 clusters of this locality are necessary to equal a normal 
cluster. The number of the fresh clusters, estimated at about 400, thus 
has to be reduced to about 250. The number of apparently living eggs 
in this locality therefore decreased, after the wilt had operated, to 
about 42 per cent.^ 

1 This forest was cut down by the owner in the beginning of the winter of 1910-11, and all egg 
clusters which the forest contained were collected by the local superintendent; 444 clusters were 
found. Our estimate of the clusters in the autumn, which was 400, therefore was nearly correct. 
The number of apparently living eggs which remained after Flacherie did its work has to be in- 
creased 3 per cent., that is to say, to 45 per cent. 



29 



Boxford, Mass. 

Division Agent, Francis C. Worthen; Assistant Local Superintendent, Harry 

L. Cole. 

Two places were selected in the West Boxford district for the in- 
tended exi^ei'lments. The locality which we shall consider first is situ- 
ated opposite the almshouse, near the Almshouse Road, and is only 
about a quarter of an acre in size. This small isolated wood is com- 
posed of oaks almost fifty to sixty years of age, and there is no brush. 
The gypsy moth caterpillars Avere numerous here in the summer of 
1909. No disease had been noticed among them, according to Mr. 
Worthen and Mr. Cole, nor have any artificial means of destroying the 
gypsj' moth been undertaken here. Mr. Worthen and I estimated the 
number of egg clusters at the time of my first visit, on May 6, 1910, 
at about 200. 

Mr. Cole was intrusted with raising the caterpillars for the Boxford 
experiments. Having received no notice of the wilt making its appear- 
ance in the brood, on the 14th of June, 1910, I went to Boxford to 
inspect the material. It was found that Mr. Cole had reared the 
caterpillars in a very cold cellar, where they were eating but little 
and were retarded considerably in their development. He was in- 
structed to place the caterpillars immediately in a warmer place in the 
open air. On June 19, 1910, a letter from him announced that 
Flacherie had broken out in his brood. On June 21 I went to Boxford 
to confirm his statement. About 5 per cent, of the caterpillars of this 
brood had already died of Flacherie, and most of the individuals still 
living showed all the signs of the disease. 

One part of this brood was exposed, with the assistance of Mr. Cole, 
on the same day in the western part of the selected locality. The bag 
containing the material was fastened between twigs of oak trees, about 
6 feet from the ground. Most of the caterpillars of this locality were 
at this time about ready for the fourth molt. 

The fresh clusters at this place were estimated, on Aug. 26, 1910, 
by the division agent and myself, to be about 60. The first 5 clusters 
which were found were collected and examined. The examination re- 
sulted as follows : — 

Cluster 1. 

Unfertilized eggs, ■ ■ ■ -\ . ^^ i. Uic + 

T-> -xi J- J t- /. / = 4.92 per cent., or about 5 per cent, 

liiggs with dead embryos, . 6 J 

Eggs apparently aUve, . .116 =95.08 per cent., or about 95 per cent. 
Total, . . . .122 eggs. 



30 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 



Cluster 2. 

,r, \ =10.16 per cent., or about 10 per cent. 
115 =89.84 per cent., or about 90 per cent. 

128 eggs. 



Total, 



Cluster 3. 
3 I 
. ) = 7.14 per cent., or about 7 per cent. 

91 =92.86 per cent., or about 93 per cent. 
98 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Cluster 4- 

8 1 
^P ; =28.24 per cent., or about 28 per cent. 

61 =71.76 per cent., or about 72 per cent. 
85 eggs. 

Cluster 5. 
Unfertilized eggs, • . . - 1 „ ^„ , r. 

Eggs with dead embryos, . 5 / = ^'^^ P^' '^°*-' «' ^^°"* ^ P"'" «^^*- 
Eggs apparently aUve, . . 164 =97.04 per cent., or about 97 per cent. 

Total, . . . .169 eggs. 

The average of these 5 clusters gives the following result : — 

Dead eggs, . . . . 11 = 9.17 per cent., or about 9 per cent. 
Eggs apparently alive, . . 109 =90.83 per cent., or about 91 per cent. 



Total, 



. 120 eggs. 



Since this place, weakened by the wilt, contained only 109 eggs with 
apparently living embryos to the cluster, almost 4 clusters were neces- 
sary to equal the size of a normal cluster. The number of fresh egg 
clusters, which were estimated at 60, thus must be reduced to about 
20 clusters. The number of apparently living eggs was therefore de- 
creased, as the result of Flacherie, to about 10 per cent. 

The second place which was selected in West Boxford for exjoeri- 
ments Avith the disease consists of an isolated wood of about half an 
acre. Most of the trees are oaks about thirty years of age, mixed 
with underbrush. This locality is situated on Highland Street, between 
two apple orchards. In the summer of 1909 the gypsy moth cater- 
pillars A^'ere relatively more numerous than at the first place. No dis- 



31 



ease was noticed among- them by Messrs. Worthen and Cole, but it is 
nevertheless possible that the wilt might have made its apjiearance. 
No ai'tifieial means for destroying tlie gypsy moth had been undertaken 
here. The number of egg clusters present at the time of my first visit 
in the spring of 1910 was estimated by Mr. Worthen and myself at 
about 550. 

Flaeherie, Avhieh had been develojied artificially by Mr. Cole, was 
planted in (his locality June 21, 1910, in the same manner as in the 
place first described. The cateri^illars were about ready for the fourth 
molt, as in the first experiment. With the assistance of the division 
agent the fresh clusters at this locality were estimated on Aug. 26, 
1910, to be about 80. The microscopical examination of the first 5 
clusters found shows : — 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 1. 



10 



= 6.67 per cent., or about 6.5 per cent. 



154 =93.33 per cent., or about 93.5 per cent. 
165 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Cluster 2. 

= 6.25 per cent., or about 6 per cent. 
90 =93.75 per cent., or about 94 per cent. 

96 eggs. 



Cluster 3. 

2 1 

_, ) = 7.09 per cent., or about 7 per cent. 

per cent. 



118 =92.91 per cent., or about 93 



127 eggs 



Cluster 4- 

3 \ 
■•c, ( = 9.68 per cent., or about 9.5 per cent. 

. 140 =90.32 per cent., or about 90.5 per cent. 
. 155 eggs. 



Cluster 5. 
This cluster proved to be entirely without eggs, and it consisted only of a 
mass of wool of about 1 square centimeter in size. The female moth, which 
deposited this cluster, seems to have been absolutely sterile. It started 
mechanically, it is true, to lay eggs, but of course it coiild deposit nothing 
except the hairs from its abdomen. 



32 

The average of these ehasters gives the following result : — 

Dead eggs, .... 8 = 7.34 per cent., or about 7 per cent. 
Eggs apparently alive, . . 101 =92.66 per cent., or about 93 per cent. 

Total, . . .109 eggs. 

Since this locality, which had been infected with the wilt, showed 
only 101 eggs with apparently living embryos on the average per 
cluster, about 4 clusters would be equal to a normal one. The fresh 
egg clusters, which were estimated at about 80, thus have to be re- 
duced to about 20. The number of apparently living eggs in this 
infested locality has thus decreased to about 4 per cent. 

A third locality in which the wilt appeared naturally was somewhat 
closely inspected. A small isolated wood of about 3,000 square feet 
is situated on Main Street, about 500 yards south of Wood's Corner. 
The trees consist of oaks a hundred years or more of age, and the 
place is free from underbrush. The gypsy moth caterpillars were very 
numerous here in the summer of 1909, but no definite statement can 
be made as to whether or not there was disease among them. If the 
disease was present, it was doing little harm, as otherwise dead cater- 
pillars in large numbers would have been noticed, without doubt, by 
the division agent or the local superintendent. Mr. Worthen estimated 
the number of clusters present in the spring of 1910 at about 400. No 
artificial means for destroying the gypsy moth were undertaken. Meas- 
ured in a straight line this place is at least 1 mile from the nearest 
of the two localities previously mentioned. Flacherie was noticed here 
at a time when most caterpillars were in the fourth molt. Here, too, 
the disease worked considerably among the caterpillars. It was hard 
to find even 50 clusters when Mr. Worthen and I estimated the freshly 
laid ones, on Aug. 26, 1910. For comparison the first 5 clusters found 
were collected and examined. They gave the following results : — 



Cluster 1. 
Unfertilized eggs, . . . - 1 

Eggs with dead embryos, . g / = ^ ^ "^^ P^^ ^^nt., or about 1 1 per cent. 
Eggs apparently alive, . . 63 =88.73 per cent., or about 89 per cent. 

Total, .... 71 eggs. 

Cluster 2. 
Unfertilized eggs, . . . 1 1 

Eggs with dead embryos, . 10 / = ^^'^^ P^" '^^*-' «" ^^^^^ ^^ P^^ ^<^"<^' 
Eggs apparently alive, . . 96 =89.72 per cent., or about 90 per cent. 

Total, . . . .107 eggs. 



33 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 

Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 
The average of these 

Dead eggs, 

apparently alive, . 

Total, 



Cluster S. 

2\ 

Q } = 6.94 per cent., or about 7 per cent. 

134 =93.06 per cent., or about 93 per cent. 



144 eggs. 

Cluster 4- 



4.26 per cent., or about 4 per cent. 
90 =95.74 per cent., or about 96 per cent. 

94 eggs. 
Cluster 6. 



19 f ~ ^"^^ P^'' cent., or about 8.5 per cent. 
. 149 =91.41 per cent., or about 91.5 per cent. 

. 163 eggs. 

5 clusters gives the following result : — 

9 =7.08 per cent., or about 7 per cent. 
. 106 =92.92 per cent., or about 93 per cent. 

. 115 eggs. 



Thus in this locality, also, in which the wilt appeared naturally, the 
egg clusters were far below the normal size. Examination showed that 
about 4 of these clusters would be necessary to equal a normal one 
in size. The estimated sum of -50 clusters, therefore, must be reduced 
to about 14. Hence, the apparently living eggs which remained amount 
to about 4 per cent. 

Finally, a forest of about 30 acres was inspected. This is situated 
at an angle of 4.5°, and half a mile distant from the two first localities. 
In this forest, which consists mainly of large pines and oaks, the gypsy 
moth caterpillars had been present in considerable numbers during 
the summer of 1909, and were still more numerous during the 
first part of the summer of 1910. The owners of this place intended, 
according to the division agent, to cut down the forest, thus preventing 
a total stripioing and decrease of the value of the wood. A powerful 
ally came to the support of the owners during the latter part of the 
summer of 1910, in the g-uise of Flacherie, which cleared up the cater- 
pillars in a manner that left nothing to be desired. It cannot be deter- 
mined whether the disease appeared naturally or was spread to this 



34 

forest from the two localities in which the experiments were performed. 
However this may be, the wilt had acted at any rate in such a virulent 
manner that in all these 30 acres of forest not a single fresh egg cluster 
could be found, notwithstanding the most painstaking search on the 
part of Mr. Worthen and myself. 

Mr. Worthen also undertook, on his own behalf, the breeding of sev- 
eral hundred caterpillars, feeding them according to my instructions. 
The disease could be noticed in this brood as early as June 14, 1910. 
Most of these caterpillars had just passed the third molt. Three days 
later he exposed all the material among the caterpillars of a forest near 
his home. Soon he observed the " dying off " of the caterpillars which 
were there present. The number of the dead ones grew astonishingly, 
but the final result cannot be stated, since, unfortunately, the trees 
were later sprayed with arsenate of lead. 

West Bedford, Mass. 

The division agent and the local superintendent in this locality were 
not requested to perform the experiments. My friend, Mr. L. W. 
Swett, the well-loaown specialist in Geometridae, asked me in the spring 
of 1910 to undertake an experiment with the wilt upon his estate on 
Davis Street, northeast of the railroad station, in West Bedford. We 
inspected the place for this purpose on May 29, and the locality ap-. 
peared to be a very suitable one for the Avork. It consists of two iso- 
lated strips of wood, which meet at a right angle. One strip comprises 
oaks about fifty years of age, mixed with some brvish; while the other 
consists of dense birch brush about six years old. The whole locality 
comprises about three-quarters of an acre. The gypsy moth was first 
discovered here in 1908, and the place since that time has been under 
continuous observation by Mr. Swett. He assured me that there were 
positively no signs of a disease among the caterpillars. During the 
summer of 1909 the caterjDillars were quite numerous. Part of the egg 
clusters, which were laid in the autumn of 1909, were killed with 
creosote, but there were still present, according to Mr. Swett's and my 
estimation at the time of my first visit, about 400 clusters on the oaks 
and about 100 clusters on the birches. 

The caterpillars for this experiment were raised by the author at 
Forest Hills. They began to die from Flacherie after a continuous 
feeding of fourteen days, and just as they had passed the third molt. 
This material was planted, June 22, 1910, in the birch brush, and the 
bag was fastened about 6 feet from the ground. Most of the cater- 
pillars of this locality were at that time half way between the third 
and fourth molt. The place was visited again on July 18, 1910, to 
determine the progress of the disease. Mr. Swett and I found that 
the caterpillars were dying in considerable numbers, and the percentage 
of dead individuals was greatest on the shortest brush, and decreased 



35 



gradually the higher the vegetation grew. For instance, all the eater- 
pillars which had been feeding on the small willow brushes were already- 
dead. This brush, hardly 3 feet high, occurs here and there in front 
of the two rows of woods. The dead caterpillars were readily seen, 
as they were hanging all over the brush. Many of the caterpillars on 
the birches were dying, but a considerable number of living individuals 
was still present. In the colony of the high oaks, however, the wilt had 




Fig. 3. — Experiment, West Bedford, Mass. A. Dense birches. X- Exposure of 
disease. B. Oaks and underwood. C. Field. D. Marsliy meadow with a few 
scattered willows. 



not spread so much, although dead individuals were found in consider- 
able numbers. 

On Sept, 23, 1910, the freshly laid egg clusters were estimated. We 
made the interesting discovery that there existed no fresh clusters in 
the row overgrown with birch. Thus, all the caterpillars, at least the 
females, had been killed by Flacherie. To be certain of this fact the 
crevices of the bordering stone wall were carefully examined, since 
the gypsy moth female selects with preference such hidden places for 
oviposition. But no fresh clusters could be found here. The other row 
with the high oaks, however, proved to have a relatively large number 



36 



of fresh clusters, which were estimated at about 150. Mr. Swett later 
made an examination and confirmed these facts. There is no sufficient 
explanation so far for the jjeculiar behavior of the wilt in this locaUty. 
Apparently the wind here played a special role. The difference in the 
vegetation may also have had some influence. Does the eating of birch 
foliage hasten the ijroduetion of the disposition to Flacherie among 
the caterpillars? 

The accompanying map will complete the description of the West 
Bedford locality (Fig. 3). 

The microscopic examination of the 5 first egg clusters, found on 
the oaks, gave the following result : — ■ 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 1. 



(. ) = 2.69 per cent., or about 2.5 per cent. 
181 =97.31 per cent., or about 97..5 per cent. 

186 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 2. 

- ) = 2.67 per cent., or about 2.5 per cent. 
328 =97.33 per cent., or about 97.5 per cent. 

337 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 3. 

. ) = 3.25 per cent., or about 3 per cent. 
149 =96.75 per cent., or about 97 per cent. 

154 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, . . 



Cluster 4. 



12 



f.Q ( =20.65 per cent., or about 20.5 per cent. 
269 =79.35 per cent., or about 79.5 per cent. 

339 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 5. 

Q ) = 3.19 per cent., or about 3 per cent. 
303 =96.81 per cent., or about 97 per cent. 

31J 



37 

The average of these 5 clusters gives the following result : — 

Dead eggs, . . . . 20 = 7.52 per cent., or about 7.5 per cent. 
Eggs apparently alive, . . 246 =92.48 per cent., or about 92.5 per cent. 

Total, . . .266 eggs. 

Since this locality, in -which the wilt has worked, contained only 
246 eggs with apparently living embryos in average per cluster, nearly 
2 clusters were necessary to equal a single normal cluster. The num- 
ber of fresh clusters, which were estimated at about 150, must therefore 
be reduced to about 90. The number of apparently living eggs of that 
part of this locality which bears the oaks was therefore decreased to 
about 22.5 per cent, after the wilt had worked, while, as already men- 
tioned, the iDart with the birches contained probably no living eggs. 

Haverhill, Mass. 

Division Agent, H. F. Armstrong; Local Superintendent, G. F. Moore. 

With the assistance of the local superintendent a place was selected 
for the experiment in East Parish, Haverhill; it is situated west of 
East Broadway and northeast of Millway Pond, and on the Old Coun- 
try Koad. This locality represents almost 50 acres of isolated forest, 
in which oaks about thirty years old, mixed with underbrush, prevail. 
Only about 12 acres of this forest are infested with the gyi^sy moth. 
The caterpillars were numerous here during the summer of 1909, but no 
disease was present, according to the local superintendent. On May 
18, 1910, our joint estimation gave 1,000 clusters per acre, i.e., alto- 
gether about 12,000 clusters. No artificial means of destroying the 
gypsy moth had been undertaken. 

Mr. Moore, owing to lack of time, could not raise caterpillars for 
the experiment, and he had no reliable man to whom he could entrust 
the work. Upon the recommendation of Mr. Fitzgerald, the field in- 
spector of the northern divisions, the brother of the local superin- 
tendent of Methuen, Mass., Mr, Wagland, was intrusted with the raising 
of the caterpillars. As no communication was received from Mr. Walter 
Wagland by June 21, 1910, that his caterpillars showed signs of 
Flacherie, I went on this day to Methuen, to convince myself of the 
condition of the insects. The local superintendent, A. H. Wagland, 
Mr. Walter Wagland's brother, was with me, and we found that all 
the caterpillars were sick and that several had already died. The reason 
why I had received no word from Mr. Walter Wagland was that he 
did not recognize the disease. The planting of the material in the se- 
lected place in Haverhill was accomplished the next day. All the 
material was exposed in a pasteboard box in the western part of the 
forest, about 6 feet from the ground and between limbs of oak trees. 



38 



Most of the caterpillars of this locality were at this time about half 
way between the third and fourth molts. 

The place was visited again Aug. 30, 1910. with the local superin- 
tendent of Haverhill, to see how the wilt had operated, and how many 
fresh egg clusters were present. First it was noticed that the infested 
portion of the forest was not uniformly infected with Flaeherie. While 
the periphery of the infested area (about 8 to 9 acres) showed a very 
considerable decrease of the egg clusters in comparison with those of 
the spring of 1910, the real center of the colony, which covered 3 to 
4 acres, had been more resistant to the disease, although here also 
the number of the fresh clusters had decreased considerably in eom- 
, parison with the clusters of the previous year. Altogether the num- 
ber of fresh clusters of the whole colony was estimated by us to be 
about 3,500. The 5 clusters which served for examination proved to 
be as follows : — 



Unfertihzed eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 



Total, 



Unfertilized eggs, . 
Eggs with dead embrj^os. 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Cluster 1. 

20 } =28.57 per cent., or about 28.5 per cent. 
90 =71.43 per cent., or about 71.5 per cent. 

126 eggs. 

Cluster 2. 

(. \ = 3.31 per cent., or about 3 per cent. 
146 =96.69 per cent., or about 97 per cent. 

151 eggs. 



Cluster 3. 
4 

285 =94.37percent., or about 94 

302 eggs. 



5.63 per cent., or about 5.5 



per cent. 
5 per cent. 



Cluster 4. 



7l 
gc f =12.36 per cent., or about 12 per cent. 

227 =87.64 per cent., or about 88 per cent. 
259 eggs. 
Cluster 6. 

n \ = 1.95 per cent., or about 2 per cent. 
'98 per cent. 



. 302 =98.05 per cent., or about 



308 eggs. 



39 

The average of these 5 ekisters gives the following result : — 

Dead eggs, . . . . 19 = 8.30 per cent., or about 8 per cent. 
Eggs apparently alive, . . 210 =91.70 per cent., or about 92 per cent. 

Total, . . .229 eggs. 

Since a normal cluster contains, on the average, 433 eggs with ap- 
parently living embryos, and this locality in which Flacherie had pre- 
vailed contained only 210 eggs with apparently living embryos on the 
average per cluster, 2 clusters were necessary to equal a normal one. 
The number of fresh clusters, which were estimated to be about 3,500, 
must therefore be reduced to about 1,750. The number of apparently 
living eggs had decreased in this locality, after the wilt had operated, 
to about 14.5 per cent. 

Marshfieldj, Mass. 

Division Agent, John A. Farley; Local Superintendent, P. R. Livermore. 
I did not visit this locality, but the experiment was undertaken by 
the local superintendent with the assistance of Mr. Joseph Shermann 
of Marshfield, who raised the caterpillars according to my instructions. 
On visiting Marshfield on June 24, 1910, it was found that Mr. Sher- 
mann's caterpillars, most of which were ready to undergo the fourth 
molt, were sick with Flacherie. He was instructed to expose the ma- 
terial, with the assistance of the local superintendent, in a forest in- 
fested with the gypsy moth. This was done on June 26, 1910, in a 
forest of 10 acres. On Oct. 25, 1910, the local superintendent sent, 
upon my request, a number of fresh egg clusters from the locality 
where the disease had been i3lanted, and he remarked that the number 
of egg clusters were considerably decreased in comparison with those 
present in the spring of 1910. Unfortunately, further detailed eom- 
' munications regarding this locality were not received. The first 5 
clusters, which were taken from the top of the shipment, were exam- 
ined microscopically. The result was as follows : — 

Cluster 1. 

TTi -iu J J ' u irv f = 4.26 per cent., or about 4 per cent. 

Figgs with dead embryos, . 10 J 

Eggs apparently alive, . . 247 =95.74 per cent., or about 96 per cent. 
Total, .... 258 eggs. 

Cluster 2. 

Unfertilized eggs, . . . Sl,^^^, ^ i_^ior 

T-i VLi 1 J t_ r-r ) =13.47 per cent., or about 13.5 per cent. 

Eggs with dead embryos, . 65 J 

Eggs apparently alive, . . 469 =86.53 per cent., or about 86.5 per cent. 
Total, .... 542 eggs. 



40 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently aUve, . 



Cluster 3. 

2\ 
A-i)= 10.59 per cent., or about 10.5 per cent. 

363 =89.41 per cent., or about 89.5 per cent. 
406 eggs. 
Cluster 4- 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



-,a\= 5.28 per cent., or about 5 per cent. 
269 =94.72 per cent., or about 95 per cent. 

284 eggs. 

Cluster 5. 



q ) = 6.64 per cent., or about 6.5 per cent. 
181 =93.36 per cent., or about 93.5 per cent. 

194 eggs. 



The average of these 5 clusters elves the foUowina: result; 



Dead eggs. 

Eggs apparently alive. 

Total, 



31 = 9.20 per cent., or about 9 per cent. 
306 =90.80 per cent., or about 91 per cent. 

337 eggs. 



After the wilt had operated in this locality the size of the egg clusters 
was not up to the average size of the normal cluster, and the percentage 
of dead eggs was very high. 

Kingston, Mass. 

Division Ageyit, John A. Farley; Local Superintendent, C. C. Fatjnce. 

With the help of the field inspector, Mr. Norman Souther of Bridge- 
water, two places were selected for the intended experiments. The lo- 
cality which we will first consider is an isolated part of the so-called 
" Rocky Nook," and is situated about 1 mile east of the Kingston- 
Plymouth car line. This place is about a quarter of an acre in size 
and mainly overgrown with oaks about twenty-five years of age. The 
gypsy moths were discovered here in the autumn of 1909 by finding egg 
clusters. The youth of the colony made it seem improbable that there 
was any disease among the caterpillars of 1909, and, moreover, the 
egg clusters had a considerable size. Several of the clusters found 
had been killed with creosote, but there were still left about 60 clusters, 
according to Mr. Souther's and my estimate. 



41 



The local superintendent was intrusted by Mr. Souther with the 
breeding- of caterpillars. On June 24, 1910, I found the wilt in this 
brood. The same day, with the assistance of the local superintendent, 
one part of the material was exposed in the locality mentioned. This 
brood was thoroughly sick, but the " dying off " of the caterpillars had 
not begun. The bag containing the material was fastened between 
twigs about 7 feet from the ground. The caterpillars in this locality 
were at this time half way between the third and fourth molt.^ 

On Oct. 25, 1910, the fresh egg clusters of this locality were esti- 
mated by the local superintendent and myself. We found that the 
place contained almost the same numbers of clusters as in the spring 
of 1910. with the difl'erenee, however, that many clusters had the hairy 
covering only in part. Several clusters completely lacked this covering. 
It seems that the disease spread very slowly, and that it did not kill 
many caterpillars but had merely given them a mild form of the dis- 
ease, which manifested itself later in the manner mentioned, when the 
females laid their eggs. The 5 clusters which were first found were ex- 
amined, like those of other localities. The examination gave the fol- 
lowing interesting results : — 



Cluster 1. 



Unfertilized eggs, ... 2 
Eggs with dead embryos, . 13 
Eggs apparently aUve, . . 363 



= 3.97 per cent., or about 4 per cent. 
= 96.03 per cent., or about 96 per cent. 



Total, 



Unfertilized eggs, , 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently ahve, . 

Total, 



. 378 eggs. 

Cluster 2. 

Q2 I ~1S-S^ P^^ cent., or about 19 per cent. 
. 422 =81.15 per cent., or about 81 per cent. 

. 520 eggs. 

Cluster 3. 

-o ) =13.48 per cent., or about 13.5 per cent. 
. 385 =86.52 per cent., or about 86.5 per cent. 

. 445 eggs. 



Cluster 4- 



Unfertilized eggs, ... 1 
Eggs with dead embryos, . 123 
Eggs apparently aUve, . . 467 



= 20.98 per cent., or about 21 per cent. 
= 79.02 per cent., or about 79 per cent. 



Total, 



591 eggs. 



' This experiment was intentionally undertaken with sick caterpillars only, and no dead ones, 
in order to see what effect the exposure of only sick individuals might have upon the healthy 
caterpillars in the field. 



42 



Cluster 5. 

Unfertilized eggs, ■ ■ ■ -\ ^ ca ^ u^p ^ 

T-. -0.1- J J u c^ ) = 6.06 per cent., or about 6 per cent. 

Eggs with dead embryos, . 2 J 

Eggs apparently alive, . . 31 =93.94 per cent., or about 94 per cent. 

Total, .... 33 eggs. 

The average of these 5 ekisters gives the following result : — 

Dead eggs, . . . 60 = 15.23 per cent., or about 15 per cent. 

Eggs apparently alive, . 334 = 84.77 per cent., or about 85 per cent. 

Total, .... 394 eggs. 

Since this place, in which Flacherie had operated, contained on the 
average only 334 eggs with apparently living embryos per cluster, the 
size of these clusters was about one-quarter less than normal. The fresh 
clusters, which were estimated to be about 60, i.e., the same number 
which was found in the spring, thus must be reduced to about 45. The 
number of apparently living eggs of this locality therefore was de- 
creased, after the wilt had worked, to about 77 per cent. 

This experiment also shows that the exposure of sick instead of dead 
caterpillars contributes to the spread of the wilt. As in such eases, 
however, the disease spreads slowly, the caterjDillars, it is true, will not 
be killed in large numbers, but they will be infected more or less 
lightly. The result is that a high percentage of the eggs deposited 
by the females will fail to hatch. 

The second place which was selected in Kingston for an experiment 
is situated on the eastern side of Jones River, oiiposite the poor farm. 
This is an isolated wood of about one-eighth of an acre in size, which 
contains several large oaks and underbrush. The gypsy moth was dis- 
covered here also by the finding of egg clusters first in the autumn of 
1909. It cannot be stated whether disease was present among the cater- 
pillars of the summer of 1909, but this seems improbable, owing to the 
youth of the colony. Several of the clusters were killed with creosote, 
but there were still left, according to Mr. Souther's estimate, about 
50 clusters. 

The planting of the sick material was accomplished on the same 
day and in the same manner as in the first locality. Estimating the 
fresh clusters on Oct. 25, 1910, unfortunately I found that most of 
these fresh clusters (about 25) had been already killed with creosote 
by the men working under the local superintendent. Even with the 
assistance of the local superintendent, only 2 untouched Q^g clusters 
could be found. Only 1 of these could be collected, since the second 
was out of reach. Although, therefore, we are unable to draw any 



43 

complete and final conclusions in regard to the work of the wilt in 
this locality, nevertheless the result of the examination of the single 
cluster which could be secured may be given : — 

Unfertilized eggs, ... 1 1 

Eggs with dead embryos, . 12 / = ^"^^ per cent., or about 3.5 per cent. 

Eggs apparently alive, . . 356 =96.48 per cent., or about 96.5 per cent. 
Total, . . . .369 eggs. 

All we can say concerning this locality is that through the operation 
of Flacherie, which was introduced by sick material only, the number 
of fresh clusters seems to have been reduced in comparison with that of 
the previous year. 

Brockton, Mass. 

Division Agent, L. W. Hodgkins; Local Swperintendent, E. Moltan. 

The place which, with the assistance of the inspector, Mr. Norman 
Souther of Bridgewater, was selected for an experiment, is situated 
near Oak Street, northwest of Brockton Center and east of the Dutch- 
land Farm. The place, of about half an acre, consists of a growth 
of oaks about forty to fifty years of age; no brush is present. The 
caterpillars of the gypsy moth were abundant here in the summer of 
1909, but no disease was noticed among them. Several of the clusters 
were killed with creosote during the winter of 1909-10. The clusters 
which were left were estimated by Mr. Souther and myself to be 
about 40. 

The raising of caterpillars for the intended experiment Mr. Souther 
intrusted to Mr. Rudolph Marshall, 218 Battle Street, Brockton. On 
June 24, 1910, the brood was inspected. Several caterpillars had 
already died from the wilt and the others were found to be sick. This 
same day the whole material was ex])osed in the selected place. The 
bag was fastened between oak limbs, about 8 feet from the ground. 
Most of the caterpillars of this locality were at this time about half 
way between the third and fourth molt. 

This place was visited again on Oct. 7, 1910, with Mr. Souther, to 
determine the number of fresh clusters. But in spite of the most strenu- 
ous search there were found but 4 clusters; these were collected for 
examination. They resulted as follows :^ — ■ 

Cluster 1. 
Unfertilized eggs, ... 2 



_, -.,,,, irt I = 2.99 per cent., or about 3 per cent. 

Eggs with dead embryos, . 10 j 

Eggs apparently alive, . . 389 =97.01 per cent., or about 97 per cent. 

Total, .401 eggs. 



44 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 

The average of these 

Dead eggs. 

Eggs apparently alive, . 

Total, 



Cluster 2. 

13 1 

22 ) =11.71 per cent., or about 11.5 per cent. 

264 =88.29 per cent., or about 88.5 per cent. 
299 eggs. 



Cluster 3. 
3 1 
-,a\= 5.47 per cent., or about 5.5 per cent. 

;94 =94.53 per cent., or about 94.5 per cent 



3 

14 
294 

311 eggs. 



Cluster 4. 

2 1 
, „ > = 4.81 per cent., or about 5 per cent. 

196 =95.19 per cent., or about 95 per cent. 



2 
396 =95.19 
. 416 eggs. 
4 clusters gives the following r^ 



■esult : 



21 = 5.88 per cent., or about 6 per cent. 
. 336 =94.12 per cent., or about 94 per cent. 

. 357 eggs. 



Since this place, in which the wilt had operated, contained only 
336 eggs with apparently living embryos on the average per cluster, the 
size of these clusters was about one-fourth less than normal. The num- 
ber of the fresh clusters, which were found to be 4, must thus be re- 
duced to 3. The number of apparently living eggs of this locality 
therefore was decreased, after Flaeherie had worked, to about 7.5 per 
cent. 

Beverly, Mass. 

Division Agent, Saul Phillips; Assistant, W. F. Holmes. 
With the help of the assistant of the division agent two places were 
selected for the experiments. The place which we will first consider 
is situated near Hart Street, north of Greenwood Avenue, Beverly 
Farms. It is an isolated wood of about 1 acre, mainly overgrown with 
maple about fifty to sixty years of age, and yellow birch, and has dense 
underbrush. The gypsy moth caterpillars were very numerous here 
during the summer of 1909, but no disease was noticed among them. 
A small percentage of egg clusters was killed with creosote during the 



45 



winter of 1909-10. A joint estimate of the egg clusters in this locality 
made with the assistant of the division agent in the spring of 1910 re- 
sulted in finding about 500 clusters. 

The rearing of caterpillars was undertaken by Mr. Phillips's as- 
sistant. On June 20, 1910, he noticed the first dead individuals in 
the brood. Three days after the receipt of this communication I went 
to Beverly to inspect the material. Many of the caterpillars had 
already died from the wilt. This same day (June 25), with the help 
of the assistant, one part of the material was exposed in the western 
portion of the locality mentioned. The bag containing the material 
was fastened about 6 feet from the ground, between limbs with dense 
foliage. Most of the caterpillars of this locaUty had at this time just 
passed the third molt. 

After the wilt had operated all through the summer among the cater- 
pillars of this locality, the place was visited again on Sept. 13, 1910, 
together with Mr. Phillips's assistant. We estimated the number of 
fresh clusters present to be about 250. The decrease in the size of 
the clusters compared with' those of the previous year was very strik- 
ing. The examination of the first 5 clusters which were found gave 
the following result : — 



Unfertilized eggs, 

Eggs with dead embryos, 

Eggs apparently alive, . 



Cluster 1. 



^2 \ =13.60 per cent., or about 13.5 per cent. 
108 =86.40 per cent., or about 86.5 per cent. 



Total, 



Unfertilized eggs, 

Eggs with dead embryos, 

Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



. 125 eggs. 



Cluster 2. 



= 5.92 per cent., or about 6 per cent, 
per cent., or about 94 per cent. 



159 =94.08 



169 eggs. 

Cluster 3. 

„ \ = 7.37 per cent., or about 7 per cent. 
88 =92.63 per cent., or about 93 per cent. 

95 eggs. 

Cluster 4- 

„ > = 5.76 per cent., or about 5.5 per cent. 
131 =94.24 per cent., or about 94.5 per cent. 

139 eggs. 



46 

Cluster 5. 

Unfertilized eggs, . . . -\ „._ , i./^r j. 

_, .,,,,, a(= 6.45 per cent., or about 6.5 per cent. 

Eggs with dead embryos, . 4 J 

Eggs apparently alive, . . 58 =93.55 per cent., or about 93.5 per cent. 
Total, ... . .62 eggs. 

The average of these .5 clusters gives the following result : — ■ 

Dead eggs, .... 9 = 7.63 per cent., or about 7.5 per cent. 
Eggs apparently alive, . . 109 =92.37 per cent., or about 92.5 per cent. 

Total, .... 118 eggs. 

Since a normal cluster contains on the average 433 eggs with appar- 
ently living embryos, and this place, in which Flacherie had operated, 
contained only 109 eggs with apparently living embryos on the average 
per cluster, about 4 clusters were necessary to equal the size of a 
normal one. The number of fresh clusters, which were estimated to 
be about 250, thus must be reduced to about 65. The number of ap- 
parently living eggs of this locality therefore was decreased, after the 
wilt had worked, to about 15 per cent. 

For the second experiment, a small isolated group of oaks, about 
eighty years of age, was selected. This place is situated near the 
railroad station, Beverly Farms, between the railroad track and the 
ocean. Tlie caterpillars of the gypsy moth have always appeared here 
only in small numbers, and there were hardly more than one dozen 
clusters in the spring of 1910. according to our estimate. It must 
be mentioned, especially, that this locality is always exposed to very 
strong winds. 

Flacherie, artificially developed by the assistant of the division agent, 
was planted among the caterpillars at this place on June 25, 1910, in 
the same manner as in the first locality. Considering the heavy breeze 
the material was placed in a wooden box, which was then fastened 
between limbs; thus the wind was not able to carry off the whole 
material. Most of the caterpillars of this place were about ready 
at this time to undergo the third molt. 

On Sept. 13, 1910, this locality was visited again. The wilt had 
done very considerable damage to the caterpillars. Although the place 
was carefully searched with Mr. Holmes's assistance, we could find but 
2 fresh clusters. One of these is especially remarkable, as it lacks com- 
pletely the protecting covering. The microscopic examination of both 
clusters gave the following results : — 



47 



Cluster 1. 
Unfertilized eggs, ■ • ■ 3 1 ^ , _ , 

Eggs with dead embryos, . 8 / = ^'^^ P^'" '"^*-' «^ ^^^^^ ^ per cent. 
Eggs apparently alive, . 109 =90.83 per cent., or about 91 per cent. 



Total, .... 120 eggs. 

Cluster 2. ^ 

Unfertilized eggs, • • • 38 \ u . o-r c 

TTi -i.-^ A A \^ lief =87.50 per cent., or about 87.5 per cent. 

Eggs with dead embryos, . 116 J ^ ' ^ 

Eggs apparently alive, . 22 =12.50 per cent., or about 12.5 per cent. 

Total, .... 176 eggs. 

The a^'era.s•e of these 2 clusters gives the following : — 

Dead eggs, .... 83 =55.70 per cent., or about 55.5 per cent. 
Eggs apparently alive, . . 66 =44.30 per cent., or about 44.5 per cent. 

Total, . . . .149 eggs. 

Since this place, in which Flacherie had operated, contained only 
66 eggs with ap])arently living embryos on the average per cluster, 
the size of these clusters was about five-sixths less than normal. The 
number of fresh clusters, which were found to be 2, thus equal together 
only one-third of a normal one. The number of apparently living 
eggs of this locality therefore had decreased, after the wilt had worked, 
to about 3 per cent. 

Cohasset, Mass. 

Division Agent, F. A. Bates; Local Superintendent, J. E. Grassie. 

An island, known as Barron's Island, which is situated southeast of 
Cohasset in the headj^art of Bailey's Creek, was selected for the ex- 
periment. This island has an area of about 10 acres, and is densely 
overgrown, mostly with oaks about twenty-five years of age and with 
underbrush. The gypsy moth was quite numerous here in 1909, but 
there was no disease among the caterpillars, according to Mr. Grassie's 
statement. Our joint estimate of the clusters which were present in 
the spring of 1910 was about 2,000. No artificial means of destroying 
the gypsy moth had been undertaken here. 

Mr. Grassie, who was intrusted with the breeding of the caterpillars, 
noticed the wilt in this brood after a feeding of about sixteen days. 
On June 27, 1910, the caterpillars were inspected, and there were found 

1 Without the protecting cover. 



48 

about 70 per cent, individuals already dead from the disease.^ The 
same day all the material was exposed, with the assistance of Mr. Gras- 
sie, in tlie western part of the selected place, and about 6 feet from 
the ground. Most of the caterpillars of this locality were at this 
time about ready to undergo the fourth molt. 

On Sept. 26, 1910, the island was visited again, in company of the 
local superintendent, to determine in what manner the wilt had op- 
erated among the caterpillars. An especially considerable reduction 
of the number of the fresh egg clusters, compared with those of the 
previous year, had not occurred. According to our estimate there were 
about 1,500 fresh clusters. The size of each of these clusters, com- 
pared with the clusters found in the spring of 1910, was diminished 
in such a degree, however, that the clusters were often no larger than 
a bean. The eggs also were often only covered in part with hair. This, 
as well as the comparatively small mortality and the smallness of the 
fresh clusters, may be perhaps a consequence of the late planting of 
the disease. It is true that a number of caterpillars were killed, but 
most of them only grew slightly sick, the disease again expressing it- 
self at the time of oviposition. The fresh clusters of this locality were 
also of an abnormally light yellowish color, which was noticed nowhere 
else. 

The examination of the first 5 clusters found gave the following re- 
sult : — 

Cluster 1. 

Unfertilized eggs, •••41 u*« *. 

TT. -iu 1 J u "7 f = 0-36 per cent., or about 6 per cent. 

Eiggs with dead embryos, . 7 J ^ ' ' 

Eggs apparently aUve, . 162 =93.64 per cent., or about 94 per cent. 

Total, . . . .173 eggs. 

Cluster 2. 

Unfertilized eggs, . . . 3 1 

TT. •*.! J J 1, Iff r =23.68 per cent., or about 23.5 per cent. 

Jiiggs with dead embryos, . 15 J ^ 

Eggs apparently alive, . . 58 =76.32 per cent., or about 76.5 per cent. 
Total, .... 76 eggs. 

Cluster 3. 

Unfertilized eggs, . . . 1 1 , ^ ^„ 

■c -iu J J u c r = 12.28 per cent., or about 12 per cent. 

Eggs with dead embryos, . 6 J ^ ' ^ 

Eggs apparently alive, . . 50 =87.72 per cent., or about 88 per cent. 
Total, .... 57 eggs. 

1 It should be mentioned that Mr. Grassie sent a telephone communication on June 12, 1910, 
that the wilt had made its appearance among his caterpillars, but by a mistake I did not receive 
this notice until June 23. 



49 



Cluster 4- 
Unfertilized eggs, ... Sl ,„„, 

Eggs with dead embryos, . 21 / = ^^'^^ P^>^ «^^*-' °^ ^^out 18 per cent. 
Eggs apparently alive, . .116 =81.69 per cent., or about 82 per cent. 

Total, .... 142 eggs. 

Cluster 5. 
Unfertilized eggs, ... 8 \ _„ , _ , 

Eggs with dead embryos, . 66/ =^^ ^^ ^^^ '^^*-' °" ^^"^^ ^^ P^'' ^^"*- 
Eggs apparently alive, . . 115 =60.85 per cent., or about 61 per cent. 

Total, . . . .189 eggs. 

The average of these 5 clusters gives the following result : — 

Dead eggs, .... 27 =21.26 per cent., or about 21 per cent. 
Eggs apparently ahve, . 100 =78.74 per cent., or about 79 per cent. 

Total, . . . .127 eggs. 

Since this place, in which Flacherie had worked, contained only 100 
egg's with apparently living embryos on the average per cluster, more 
than 4 clusters were necessary to equal a normal cluster. Thus the 
number of fresh clusters must be reduced to about 370. The number 
of apparently living' eggs of this locality therefore had decreased, after 
the wilt had operated, to about 18 per cent. 

Hingham, Mass. 

Division Agent, F. A. Bates; Local Superintendent, A. W. Young. 

For the experiment an island of about 1 acre was selected, very 
densely overgrown with low wood. This island is situated east of 
Water Street and south of the railroad track in the so-called Millpond, 
The wood consists mainly of oaks and birches of five to six years of 
age, and of underbrush. The gypsy moth was quite numerous here 
in the summer of 1909, but there was no disease among the caterpillars, 
according to the statements of the division agent and the local super- 
intendent. Several of the clusters were killed with creosote during the 
winter of 1909-10. The number of the clusters which still remained 
was estimated by Mr. Young and myself to be about 100. 

The breeding of a series of caterpillars was accomplished exactly 
according to my instructions by the local superintendent, but unfor- 
tunately he omitted to send word when the wilt made its appearance, 
since he had understood that he was to notify me only after all the 
caterpillars of the brood had died. To convince myself about the con- 



50 



dition of the brood, I inspected the caterpillars July 1, 1910, and found 
that about 60 per cent, of them had succumbed to Flacherie. The first 
dead caterpillars were noticed by Mr. Young about fifteen days before. 
On the same day the whole of the material was exposed, with Mr. 
Young's assistance, in the southwestern part of the island, about 5 feet 
from the ground. Most of the caterpillars of this locality had at this 
time just undergone the fourth molt. 

On Sept. 26, 1910, this island was visited, again in company with the 
local superintendent. We could see that the wilt had done very con- 
siderable damage to the caterpillars, for .there were only a few scattered 
clusters. According to our estimate there were hardly 15 fresh clusters 
present; these, moreover, were much smaller in size than those of the 
previous year. It was also noticed that the clusters were often only 
partly covered with hair. All these conditions may well be attributed 
to Flacherie. The almost full-grown caterpillars had contracted the 
disease, and the females which then emerged from pupae produced by 
these caterpillars were unable to oviposit like healthy moths. 

The examination of the first 5 clusters found gave the following re- 
sult : — 

Cluster 1. 

Unfertilized eggs, ... 3\^_^ ^ , , r^ ^ 

T-i -^T. J J u ir> f = 9-5d per cent., or about 9.5 per cent. 

Eggs with dead embryos, . 10 J ^ ^ 

Eggs apparently alive, . . 123 =90.44 per cent., or about 90.5 per cent. 
Total, . . . .136 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



Cluster 2. 



.. „ > = 8.82 per cent., or about 9 per cent. 
155 =91.18 per cent., or about 91 per cent. 



Total, 



170 eggs. 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



UnfertiUzed eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



Total, 



Cluster 3. 

„ } = 4.73 per cent., or about 4.5 per cent. 
161 =95.27 per cent., or about 95.5 per cent. 

169 eggs. 

Cluster 4' 

2 \ 

r ( =10.77 per cent., or about 10.5 per cent. 

58 =89.23 per cent., or about 89.5 per cent. 
65 eggs. 



51 



Cluster 5. 
Unfertilized eggs, • • ■ 4 \ „ „^ 

Eggs with dead embryos, . 9 / = ^'^^ P^'' ^^"*-' °' ^^out 9 per cent. 
Eggs apparently alive, . . 128 =90.78 per cent., or about 91 per cent. 

Total, . . . .141 eggs. 

The average of these 5 clusters gives the following result : — 

Dead eggs, . . . . 11 = 8.09 per cent., or about 8 per cent. 
Eggs apparently alive, . . 125 =91.91 per cent., or about 92 per cent. 

Total, . . . .136 eggs. 

Since this place, in which Flacherie had operated, contained only 125 
eggs with apparently living embryos on the average per cluster, almost 
4 clusters were necessary to equal a normal one. The number of the fresh 
clusters thus must be reduced to about 5. The number of apparently 
living eggs of this locality therefore had decreased, after the wilt had 
worked, to about 5 per cent. 

By field, Mass. 

On June 30, 1910, a letter was received from Mr. James 0. Hale 
of Byfield, in which he stated that he had heard of my Flacherie ex- 
periments of 1909, and asked for aid in diminishing the gypsy moth 
caterpillars by using Flacherie. I therefore visited the locality on 
July 5, 1910, and took with me sick and dead caterpillars which had 
been raised at Forest Hills. The forest in question is about 4 to 5 
acres in size, and consists mainly of oaks of different ages and some 
underbrush. It is situated on the border between Rowley and Newbury. 
It is not isolated, but connected with woods which belong to other 
persons. At the time of my arrival most of the caterpillars had already 
undergone the fifth molt, so that it seemed questionable whether the 
disease would be able to show much success this year. The infected 
material was exposed in the southwestern part of the forest, about 
7 feet from the ground. It proved to be impossible to secure a correct 
estimate of the caterpillars which were present; all that could be stated 
was that the caterpillars were quite plentiful. 

This locality was visited again with Mr. Hale on Sept. 16, 1910, to 
determine the results. Mr. Hale gave his opinion that there was, at 
the least, no increase in the number of egg clusters compared with that 
of the previous year, although there was no visible decrease in the 
number of the fresh clusters. However, these fresh clusters were con- 
siderably smaller than those of the preceding year. 

The first 5 clusters collected gave the following counts : — 



52 



Unfertilized eggs, 

Egga with dead embryos, 

Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 



Total, 



Unfertilized eggs, . 
Eggs with dead embryos. 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Unfertilized eggs, . 
Eggs with dead embryos, 
Eggs apparently alive, . 

Total, 



Cluster 1. 

21 

C \ = 8.33 per cent., or about 8 per cent. 

88 =91.67 per cent., or about 92 per cent. 
96 eggs. 



Cluster 2. 

t\= 3.76 per cent., or about 3.5 per cent. 
128 =96.24 per cent., or about 96.5 per cent. 

133 eggs. 

Cluster 3. 

p. / = 2.75 per cent., or about 2.5 per cent. 
212 =97.25 per cent., or about 97.5 per cent. 

218 eggs. 

Cluster 4- 

2\ 

. ) = 4.72 per cent., or about 4.5 per cent. 

95.5 per cent. 



121 =95.28 per cent., or about 95 
127 eggs. 



Cluster 5. 

r. \ = 5.59 per cent., or about 5.5 per cent. 
152 =94.41 per cent., or about 94.5 per cent. 

161 eggs. 



The averase of these 5 clusters gives the f ollowins: result ; 



Dead eggs. 

Eggs apparently alive. 

Total, 



7 = 4.76 per cent., or about 4.5 per cent. 
140 =95.24 per cent., or about 95.5 per cent. 

147 eggs. 



We notice that the clusters of this locality in which the wilt had 
operated are far smaller than normal ones, since about 3 clusters are 
necessary to equal the size of a normal one. The percentage of dead 
eggs, however, does not attain that of other localities. 



53 



IV. Summary. 

The artificially developed Flacherie was planted, after the 
" dying off " of the breeding material had begun, among the 
caterpillars of the gypsy moth in the following localities, the de- 




Flg. 4. — Diagram showing percentage of living egg» in healthy colonies. 



tails in regard to these experiments being given in the preceding 
pages. The number of apparently living eggs was reduced to 
the following percentages : — 

Per Cent. 

Concord, Mass. (Brewster's estate), 11 

Carver, Mass. (southwest of Makepeace's cranberry bog), ... 13 

Carver, Mass. (on Wenham Street), 45 

Boxford, Mass. (near the almshouse), 10 

Boxford, Mass. (on Highland Street), 4 

West Bedford, Mass. (Swett's estate), per cent. + 22^/^ per cent. = 113^^ 

Haverhill, Mass. (west of East Broadway), 143^ 



54 



Per Cent. 

Brockton, Mass. (on Oak Street), 73^ 

Beverly, Mass. (on Hart Street), 15 

Beverly, Mass. (beside railroad track), 3 

Cohasset, Mass. (Barron's Island), 18 

Hingham, Mass. (island in the millpond), 5 

Taking the average of these results, we see that the total 
number of apparently living eggs has been decreased by intro- 
duction of the artiticially developed Flacherie to about 1-k- per 
cent. This result is shown graphically in Figs. 4 and 5, where 



m 




B 
















B 




m 
















B 




^^S 


















^^^ 






5^©^ 




B 


























B 








B 




■ 


^Avivs^c 










^^ 














^^^ 








B 




■ 












^^ 


















^^ 


B 




H 












^^ 














^^ 






B 




H 












^^^ 


















^^ 












wsovVk 


8 




S 


^^^^ 










^^ 










^^ 




XrSvxS^ 


^^ 




m 












^vvvv^ 






B 


^^ 





Fig. 5. — Diagram sliowing average percentage of living eggs alter introduction 
of tlie disease. 

1 per cent, is equal to 1 square, the cross-lined spaces repre- 
senting the percentage of dead eggs. 

Only those localities have here been tabulated on which we 
had complete data from the beginning to the end of the experi- 
ment. 



55 



V. Final Conclusions. 

The foregoing experiments prove conclusively that Flacherie 
has an injurious influence upon the prosperity of the gypsy 
moth caterpillars, this influence varying according to the man- 
ner and time of the appearance of the disease. There was 
no difference noticed in the progress of the wilt which broke 
out naturally and that of the artificially developed Flacherie. 
The latter, however, is probably the more important factor, 
for with its help we may be able to introduce the disease among 
caterpillars of localities in which the wilt, perhaps, would not 
make its appearance naturally. The infection of a place with 
sick material only seems to be, as regards the " dying off " of 
the caterpillars, less favorable for the spread of Flacherie than 
with material which already contains a number of dead indi- 
viduals. In selecting the localities in which the disease is to 
be introduced, it is unimportant whether the caterpillars of the 
gypsy moth are present in large or small numbers. It is true 
the wilt will get a stronger foothold and attain a greater viru- 
lence the larger the number of caterpillars. In places, how- 
ever, which are not badly infested, the disease will also spread 
to the healthy caterpillars, as was shown by several of the 
experiments. According to the observations, we are almost 
inclined to believe that the direction of the wind plays an 
important r(31e in spreading the disease. This opinion is 
strengthened especially by the observations made in Concord 
and West Bedford. 

Wherever the naturally as well as the artificially developed 
Flacherie occurs the female caterpillars will always succumb 
to it more readily than the male. This may perhaj^s be due to 
the fact that they require a longer time to mature than the 
male caterpillars. If, at the flying period of the moth, we visit 
such a diseased locality, — one in which during the summer 
the caterpillars were quite plentiful, — we find ourselves sur- 
rounded by male moths, which to the superficial observer 
would indicate that the wilt had caused no considerable diminu- 
tion. As soon, however, as we begin to search for adult females, 
we discover that they are present in a decided minority, and 



56 

that they are by no means in the same large proportion to the 
male moths as in localities where the disease has not occurred 
among the caterpillars. The effective result, then, will be shown 
at the time of oviposition, in the decrease of the number and 
size of the fresh clusters, compared with those of the previous 
year. To be sure, this will not always be the case ; for instance, 
in localities in which Flacherie appears very late. However, 
places infected early enough, always show as a result a diminu- 
tion in the number of the fresh clusters, sometimes to 100 per 
Q,ent. The reduced average size of the clusters also has a close 
connection with the wilt. Heretofore it has often, but errone- 
ously, been supposed that small clusters were deposited by 
small female moths, which suffered during their caterpillar 
stages from lack of food. Certainly such cases are not rare, 
but the origin of small clusters is capable of yet another ex- 
planation. For instance, in localities in which there are few 
gypsy moth caterpillars, and where there is no lack of food, but 
where the wilt has worked, egg clusters are found which are no 
larger than a pea or a bean. Such clusters contain from 4 to 12 
eggs, with embryos which are usually incompletely or not at all 
developed. In such localities it may often be recognized, from 
the volume of the abdomen, even of the freshly emerged female 
moths, which were little below the normal size, that the body 
contained only a small number of eggs. Also, in several cases 
the interior of the body was examined, and then it was found 
that the cause of the small circumference of the body was that 
the ovary was small. Females which had already oviposited and 
died were examined to see whether they contained more eggs in 
their bodies. Eggs were always found in females that had laid 
egg clusters which were only partly, or not at all, covered with 
hair. But there were sometimes found undeposited eggs in fe- 
males which had completely covered the cluster with their ab- 
dominal hairs. All this must be taken in connection with the 
wilt, for female moths from healthy colonies deposit all the eggs 
they contain, as long as they are not interrupted at the time of 
egg laying, and it does not matter whether the individuals are 
large or small. 

The most important point to be noticed is the fact that the 



57 

clusters which are found in localities in which Flacherie oper- 
ates among the caterpillars contain, on the average, a compara- 
tively high percentage of dead eggs. Hence, Flacherie has a 
direct effect even upon the next generation. If, however, the 
number and the quality of the eggs in the female adult are 
affected by the wilt, is it not then possible that the disease goes 
directly over to the eggs ? Certainly we have no direct proof 
of this at the present time, but we do know that Flacherie can 
be carried over from the caterpillar to the pupa, and from the 
pupa to the adult, and we have seen that the eggs in the ovary 
of females which come from infected colonies are influenced 
by the disease in regard to their number and vitality. In spite 
of the many investigations which have been made by celebrated 
bacteriologists in both the old and the new world, the carriers 
of the disease have not yet been determined. This shows what 
a difficult problem science has before it to solve. Although 
several scientists accept neither the heredity of the disease, 
nor believe that it can be carried over to the next generation, 
there are others (Pasteur, Fischer) who believe in its trans- 
missibility. Perhaps the disease is carried over to the follow- 
ing generation through the adult female only, in a similar 
manner to the pebrine. Perhaps, moreover, the name Flacherie 
covers several diseases, which, it is true, make their appearance 
in the same manner in the infected individuals, but neverthe- 
less are specifically distinct. One of these diseases may be 
restricted, indeed, to caterpillar and pupa only, while the other 
disease is carried over to the adult, and might possibly be in- 
herited through the female organism by the descendants. It 
may be possible to throw some light on these complicated ques- 
tions by breeding experiments, but only the investigations of the 
bacteriologist and pathologist can secure the final proof. It 
would be of the highest importance for the economic value of 
Flacherie if the inheritance of the disease could be definitely 
proved. If the wilt proves to be the direct cause for the " dying 
off " of many embryos of eggs from infected localities, death 
would be caused by the organisms of the disease themselves, 
and probably not be a result of the weak constitution of the 
female moth. The still living embryos of the same cluster will 



58 

then contain, without doubt, at least partially, the carriers of 
the disease, which, according to their number and to the con- 
stitution of the embryo, will kill, early or late, the larva after 
it has hatched. Thus Flacherie will be carried again through 
the whole ontogeny of the descendants of those individuals 
which were originally infected by the disease. In this case the 
wilt would be hereditary, and it would have by far the greatest 
possible economic value and benefit. If, however, the " dying 
off " of several of the embryos is only a consequence of the 
weak condition of the female adult, which perhaps was slightly 
infected during the caterpillar stage, then of course the guaranty 
for the wilt is not yet given for the next generation. Among 
the hatching caterpillars there will always be a considerable 
percentage of weak individuals which thus possess from the 
beginning the necessary predisposition to the disease. If, then, 
the climatic conditions develop favorably for the disease, these 
weak caterpillars will be attacked first by the wilt, but as it 
increases in virulence it will attack the stronger and healthier 
individuals. If the climatic conditions are less favorable for 
the natural appearance of Flacherie, we hope the introduction 
of the artificially developed Flacherie in the respective localities 
will transmit the disease to the weak caterpillars. Then the 
disease will operate as though it had appeared naturally. 

The existence of the wilt does not depend upon climatic 
conditions as soon as the disease is once established. It is true 
weather conditions will often be of great advantage in spreading 
the disease, but not likely to be of considerable harm. Hence, 
Flacherie, even if its nonheredity should be proved, is a factor 
of great importance to economic entomology. It will be advis- 
able to work with the wilt against the gypsy moth in large 
wooded areas of all kinds, and it has the great advantage of 
cheapness, while the spraying with arsenate of lead or with 
other poisons is expensive. A very good scheme would be to 
furnish as many trees as possible with rings of tanglefoot in 
heavily infested forest districts, and not to kill the caterpillars 
after they are gathered together under the rings, but to assist 
in this manner the more rapid spread of the wilt, since the sick 
and weak individuals thus have a greater possibility of coming 



59 

in contact with healthy caterpillars. The effect of this method 
was observed in one case during the summer of 1910. In com- 
pany with the division agent, Mr. Worthen, I came in touch 
with a locality in Boxford where gypsy moth caterpillars were 
gathered together in considerable numbers under tanglefoot 
rings. It had been decided to kill the caterpillars with burning 
oil, but I dissuaded the men from doing this by giving as my 
opinion that the wilt would make its appearance in all prob- 
ability in a few days. This assumption was right, for there 
was seen, after three days, the first signs of the disease, which 
then spread so quickly that in a few more days the caterpillars 
had succumbed. 

Perhaps it might be worth while to work with the wilt in 
different ways from those in the experiments described. There 
is, for instance, the recapitulation of the experiments of 1909 on 
a large scale. Caterpillars which had been killed by Flacherie 
were mixed with water in different ways, and the mixture was 
then either sprayed upon trees or was painted as rings around 
the trunks. One or the other of these methods may prove to be 
valuable, but the expense will be quite high, while the use of the 
simple exposure method incurs but small expense. There might 
be mentioned still another point; Dr. E. Fischer of Ziirich, 
the discoverer of the predisposition of caterpillars towards 
Flacherie, wrote me some time ago the following directions for 
developing Flacherie artificially in the field: cut some of the 
larger roots of a tree that is infested with a sufficient number 
of caterpillars, water frequently the ground around the cut 
surfaces and put into the trunk as much water as possible 
through a hole bored at an angle of about 45° to the base of 
the tree. By these means the same unhealthy food is produced 
on the tree as is otherwise obtained by the placing of twigs in 
water. It is certain that the wilt can be developed artificially 
in the manner just described, but such an experiment needs 
constant attention, and trees thus treated are, of course, de- 
stroyed. 

I doubt whether the gypsy moth will ever become extinct in 
America, but the wilt will probably produce, first, a consider- 
able reduction of the mass, and then it is to be hoped that the 



60 

insect parasites and other natural enemies will contribute in 
diminishing the pest to a minimum. I am quite convinced that 
we can apply the wilt in a systematic manner to the benefit of 
our forests, and that in so doing we shall come considerably 
nearer to a solution of the problem of destroying the gypsy 
moth. In wooded areas mainly much more attention should be 
given in future to the wilt as an aid in combating the insect, 
while for street trees, garden trees, etc., which are more easily 
managed, the eggs and caterpillars of the gypsy moth may be 
removed according to established methods. The wilt should 
eventually reduce the pest to a condition in which it can be easily 
kept in check, and prevent serious outbreaks and damage. 




PLATE I. — Egg clusters from a healthy colony. 




PLATE II. — Egg clusters from a colony where disease was 
introduced. 



* '-'t^'.-'V, 



mA 




001 424 727 0^ 




